A medical research centre in Berkshire says it’s close to synthesising an antidote to the deadly Marberg virus. An outbreak of the haemorrhagic fever killed more than 300 people in Africa last year. The Head of Research at Pangbourne Scientific Laboratory, Dr Gavin Dexter, calls the serum a major breakthrough: “We are concluding our final round of testing and the results are stunning. For too long, viruses like Marberg have baffled the medical community, but what we’ve developed at Pangbourne will change the world.” The Research Centre is owned by Mandrake Inc., a private company due to be listed on the London Stock Exchange next week, but animal rights activists have vowed to disrupt Mandrake’s first day of trading. Maude Fletcher has maintained a vigil outside the facility in Berkshire for the last six months.

Sarah and Josh play back a video recording of the news report and brief their new friend Will on events in the Wiltshire village of Cloots Coombe two years earlier where they last met Maude. Will isn’t surprised to learn that Josh is involved with ‘eco-warriors’ and they start arguing about politics until Sarah intervenes. After what happened in Antarctica, she decided to go on the offensive. Whether she likes it or not, she seems to be inextricably linked to the Book of Tomorrows, so she’s been trying to find out more about the doomsday cult known as the Crimson Chapter. They already know that Hilda Winters was involved with them, so Sarah’s research started with her. She traced the woman’s steps over the last few years as best she could and discovered a list of names, all of whom served at one time or another on Réchauffer Inc. Sarah thinks the two organisations might be one and the same and the Crimson Chapter has used Réchauffer as a front to create biological weapons. That kind of research costs hundreds of millions, which would explain why Morgane was attempting to sell uranium to the highest bidder. They must be planning to fulfil their prophecy of a cleansed Earth by creating their own doomsday weapon. Sarah reveals that she’s been contacted by Dr Dexter from Pangbourne, who claimed to be worried about what’s happening there and asking her to investigate.

Just as that moment, a car pulls up outside Sarah’s cottage - it’s Dr Dexter, meeting her as arranged. She introduces him to Josh and Will and at first he’s reluctant to talk to her in front of her friends. Eventually he explains that Pangbourne was able to make a breakthrough in the cure for Marberg after Réchauffer insisted they abandon all other project when they took over. Réchauffer Inc changed its name to Mandrake about eighteen months ago, after which Dr Dexter discovered the truth about what they did at Cloots Coombe. Mandrake needs a high profile drug to launch itself on the stock market, so they’ve been pushed into adopting extreme and unethical methods to achieve results. Dexter believes the antidote could endanger countless lives in the future, but he couldn’t simply resign because his daughter is severely autistic and she needs expensive private therapy that Mandrake funds. He approached Sarah because he has no actual proof and he needs her to bring out the truth about Pangbourne without involving him. He’s managed to sneak out a memo which proves part of his story - it confirms that the ‘success’ of the Marberg antidote was to be announced publicly regardless of the final trial results. Sarah can’t commit herself and tells him she will consider what he’s said and get back to him. Dr Dexter leaves and Will tells Sarah he thinks the man was genuine, but Josh thinks he’s simply trying to save his own skin after discovering what Mandrake was up to. Sarah realises Dexter could be linked to the Crimson Chapter himself, but Will points out he was working at the research centre even before Réchauffer took over. She asks Josh to look into Dexter’s background to see how far back his connection with Réchauffer goes and also to find out as much as he can about the Marberg virus and the antidote.

The Keeper receives a telephone call from Dexter informing her that he’s just left Sarah’s cottage but he’s not sure whether she’s taken the bait yet. Will Sullivan was also there, but he didn’t seem to suspect anything. Dexter tells her that Sarah was not what he expected and the Keeper knows that it will not be long before she meets the herald herself.

Sarah and Will go for a walk and he tells her she’s looking tired. When she admits that she hasn’t been sleeping well, he says she doesn’t need to shoulder the responsibility of fighting the Crimson Chapter alone. She points out that they’re willing to kill her and ruins the lives of the people around her, so she can’t help but blame herself. She’s at the centre of events she can’t understand or control and she’s determined to stop it. First she needs to find out who’s behind it all, so she needs someone with a medical background to help her investigate Mandrake. Will realises she means him, but he’s reluctant to become involved until she reminds him this is the sort of work his step-brother Harry used to get involved in. If Mandrake is endangering lives, they have to warn the authorities and to do that they need proof. Reluctantly he agrees, although he insists he won’t do anything to break the law. Josh joins them and tells them he’s established that Dexter’s story was true. He’s been at the centre for seven years, long before Réchauffer took over. He’s also found a record of Dexter’s daughter, so everything seems to check out. Will agrees to visit Pangbourne tomorrow, so Sarah asks Josh to speak to Maude to find out her side of the story. Sarah suspects the White Chapter probably have a good idea what the Crimson Chapter are up to, so it’s time she flushed out the other half of the Orphans of the Future!

The next day Will Sullivan arrives at the Pangbourne Research Laboratory, but he’s able to avoid confrontation with the group of animal rights protestors outside. The security officer allows him in after checking that he isn’t one of the activists trying to create a diversion and he drives up to the main entrance. Just then Josh calls out to her and they greet each other warmly. He tells her he saw her interview on the news and wanted to find out more. He’s surprised at the scale of their operation but she reminds him that you can’t maintain an outdoors vigil for six months without a degree of preparation. They discuss Mandrake’s connection to Réchauffer Inc. and she invites him to her caravan so they can fill each other in on what’s going on.

Inside they exchange information and Maude is amazed to learn that Dexter himself has apparently turned ‘whistle blower’ in protest at corners being cut. She’s sceptical as Dexter has shares in the company and is expected to become a millionaire overnight once the company goes on the market. Maude tells him her daughter Emily, who recently finished her computer science studies, has been helping the campaigners, but she had a blazing row with her last night when Emily found a confidential memo about Mandrake’s stock options after hacking their website. Maude objected to her daughter breaking the law and Emily stormed off, promising to prove her allegations about the company. Maude is worried that the protest is losing support fast, so Josh offers to ask around to see if he can find out where Emily has gone.

Sarah receives a call from Sir Donald Wakefield in Nevada. He knows she’s been trying to attract the attention of the White Chapter for the last 24 hours and he wants to know what she’s looking for. She tells him she wants answers and if she doesn’t start getting them soon, she’s going to start asking more loudly. He warns her that wouldn’t be very wise, but she refuses to be intimidated. He tells her to be at Brighton Pier in fifteen minutes and he’ll call her again. She argues that she can’t possibly get there in so short a time, but he’s not interested and hangs up.

Will is shown into Dr Dexter’s office and they pretend to ‘meet’ for the first time. Will expresses surprise at how few staff they have at such a large facility, but Dexter explains they’ve had several break-ins and death threats recently so non-essential staff were moved to other locations on police advice until the situation dies down. As Dexter gives him an injection containing a broad-spectrum immunisation, which all staff and visitors must have as a precaution, he whispers in Will’s ear that he’s to pose as the new lab assistant. They leave to visit the test subjects and Dexter explains that they’ve isolated a variant of Marberg that replicates at nearly fifty times the virus’s usual speed, which means it will incubate in hours instead of days. There are half a dozen guinea pigs and Will is expected to put on a bio-hazard suit before treating them.

Josh returns to Maude after having had a snoop around the perimeter fence. Although most of the fence is secure, he’s found a blind spot not covered by the surveillance cameras. He’s also learned that Emily and another protester called Hamish were planning to break in. It seems likely they used the blind spot, but when Maude points out that the staff would have called the police if the two of them had been caught, Josh suggests that if the company had something to hide they might beholding them prisoner. They have no proof, of course, so Josh decides it’s time to take some direct action of their own.

Will changes into the bio-hazard suit and is given instructions not to remove it. He crosses through the inner door and moves into the airlock, which features sonic sterilisers. Then he enters the test chamber where he finds a trolley containing six syringes, one for each of the test subjects. Dexter tells him the guinea pigs have suffered enough and now it’s time to cure them. Will approaches the patients and is horrified to discover they’re human beings! Dexter points out that animal testing is ineffective with Marberg and its variants, but Will can’t believe that anyone would volunteer for such a dangerous procedure. Dexter doesn’t care what he thinks - he is to administer the injections immediately or the subjects will die in excruciating agony. Will insists this is totally unethical and barbaric - and Dexter tells him the orders have come from the Keeper herself! At last Will understands and has no choice but to prove his loyalty to the Crimson Chapter by going ahead with the procedure. If he refuses, the deaths of the six patients will be on his conscience. Reluctantly, Will approaches the first patient whose name is Emily. She tells him all the patients are protestors and that Dexter is a liar. She resists the injection, but it’s no good. She begs Will to help her escape and he promises he won’t let them hurt her anymore, but Dexter reminds Will that he still have five more injections to administer.

Sarah arrives at Brighton Pier just as Sir Donald Wakefield makes his second call. He tells her she’s been brought here to meet the Keeper of the White Chapter and she turns round to find Sir Donald himself standing next to her. She’s caused his Chapter quite a lot of trouble and he‘s come all the way from Nevada to sort things out. It’s clear to Sarah that he’s quite ill and he explains that he’s still recovering from his last chemotherapy session. They sit down on a nearby bench and he explains that he’s the owner of the remaining chapters of the Book of Tomorrows and if his counterpart in the Crimson Chapter has her way, the streets will run red with the blood of millions. Both factions were convinced the aliens would return to Earth in the year 2000, but the prophecy was wrong. The Orphans of the Future were in crisis and five years ago representatives from the two groups met for the first time in a century. Scholars from both sides studied the Book and realised that a crucial part of the prophecy had been overlooked - the emergence of a human herald. They found a description and a name, which points towards Sarah. She argues there must be millions of people who match that description, but he tells her this is why it took so long to narrow the search down to her. They now know the truth and they believe that in time she will come to believe it too. Her actions in Antarctica forced the Crimson Chapter to advance their plans and unfortunately the White Chapter are ill-prepared to match them. He warns her that she’s in imminent danger and that Will Sullivan himself is an agent for the Crimson Chapter and has orders to kill her!

Will demands to know what’s going on, but Dexter points out he’s in no position to make demands. As far as Dexter is concerned, the patients broke into the facility in protest at unethical experimentation on animals, so it’s entirely acceptable for them to become the subjects instead. Time was short and they needed to check that the antidote worked. They couldn’t care less about the Food and Drug Administration and there never was going to be a stock market flotation. They have a far more pressing deadline… It’s time for Will to account for his failures! He’s ordered to enter a room where the Keeper of the Crimson Chapterhouse is waiting for him.

Sarah protests to Sir Donald - she simply can’t believe that Will is a Crimson Chapter assassin, but he plays back a tape recording of his opposite Keeper’s instructions at the end of the Antarctica disaster. She believes the tape is a fake, but he assures her they intercepted the call shortly after her return to the country. She argues that Will has had plenty of opportunities to kill her and Sir Donald agrees that he appears to be suffering from a crisis of conscience at the moment. Sarah refuses to listen to any more, but Sir Donald understand why she’s angry and confused. He implores her not to leave - there’s one more thing he needs to tell her. It doesn’t matter whether she personally believes she’s the herald, the fact remains that the Crimson Chapter does believe it. The Keeper and her acolytes regard her emergence as a call to action and have decided to manufacture their own apocalypse in keeping with their interpretation of the Book of Tomorrow. Genocide will be committed in her name, and only she can stop it!

The protestors increase their activity outside the Pangbourne research facility and Josh demands to be allowed in. He claims to have found witnesses who saw Emily and Hamish entering the building the night before (although this isn’t actually true) and Maude accuses them of keeping her daughter prisoner. When he threatens to call the police, a voice on the intercom informs them that six protestors have broken into the laboratory recently and foolishly opened the animal cages. They’re now infected with the Marberg virus and are receiving treatment. Josh recognises the voice - it’s Dexter! The doctor assures Josh that the protestors have been given the antidote and have recovered. All six have now been released and are making their way out of the building. Maude urges the other protestors to move back as their colleagues emerge from the research centre. Josh notices that they still look very ill and when Maude tries to comfort her sick daughter, he goes back to the intercom and demands to know what’s been done to them…but there’s no reply.

The Keeper tells Will he’s been brought here to explain why he failed to kill Sarah. He’d been hand picked because of his family background as someone who was perfectly placed to gain her confidence, but he points out that he wasn’t told to kill her until after he’d befriended her. He argues that he’s a physician, not a murderer. Morgane had already reported Will’s disobedience to the Keeper and she’d been instructed to compete the task in his place, yet not only did Sarah survive, she actually succeeded in ruining their entire operation in Antarctica that had taken years to set up. Their contingency project has now been forced into activation before it was ready and she hopes Dr Sullivan can live with the consequences. The Keeper adds that the White Chapter also has an acolyte who is close to Sarah who is now aware of Will’s identity and has orders to kill him! The real reason Dexter was sent to contact Sarah was to extract Will from any danger, but now both he and Josh Townsend can act as bait to lure the herald straight here. The guinea pigs have already been released, so the Keeper activates her security cameras to see how they’re doing… Will suddenly realises the truth - it wasn’t the antidote he injected the prisoners with, it was a super-accelerated variant of the Marberg virus itself! They’ll be dead within the hour…

Outside in the encampment, Maude tries to get her sick daughter to drink something, but she continues to get worse. She wavers between having a fever and being cold and now she has a rash appearing all over her body. Josh is confused as Marberg takes ten days to incubate, but he’s convinced that she’s showing all the proper symptoms. He tells Maude that Emily is dying. Soon she will start vomiting and having chest pains and then she’ll go into shock and her organs will start to shut down. At this rate, she’ll be dead very soon and with the infection moving so swiftly, so will everyone else who’s come into contact with her!

Sir Donald tells Sarah that the Crimson Chapter plan to wipe out everyone simply to prove themselves right. Only a few will survive so that the Keeper and her acolytes can “inherit the planet”. They’re willing to sacrifice everyone but themselves for their beliefs. Sarah’s phone rings - it’s Josh from outside the research centre. He tells her the protestors are dying from what looks like the Marberg virus and Sir Donald realises it’s finally started. Sarah asks him how she can stop this and he tells her she must go to the centre, because if the Crimson Chapter intends to survive this, they must have an antidote. Sir Donald will contact the Government to get the centre cordoned off to prevent the infection spreading, and he will also arrange for Sarah to be allowed access - but he reminds her that Will Sullivan is under orders to kill her.

Will protests to the Keeper - her plans to release a virus that will kill millions of people is madness. She reminds him that he pledged lifelong allegiance to the Crimson Chapter, but he points out that he did that when he was a student and just thought it was an exciting secret society. All that cloak-and-dagger stuff felt like a game but he never really believed the prophecies. The Keeper theorises that he was either envious of his brother’s work in the intelligence community or simply wanted to take the benefits that came of being a member of the organisation. Either way, he swore an oath of loyalty and she expects him to obey her without hesitation or question. He must atone for his failure or go outside to die with the others. The antidote he was given by Dexter will only last for 24 hours and without another dose he’ll be dead by tomorrow!

Maude tries to reassure Emily that help is on its way, but Josh tells her there won’t be any ambulances coming. The authorities are cordoning off the area to stop the infection from spreading because there’s no officially recognised antidote and Westminster has decided the only thing they can do is contain the outbreak. Josh suggests he go inside the research centre to find an antidote himself while Maude stays to look after Emily. Suddenly Sarah arrives and tells Josh she’s going in with him.

Dexter enquires whether everything is ready in Paris, Tokyo and Moscow. He tells his colleagues that the Keeper will give her signal within the hour and when that happens their agents across the world will break open their vials. Will arrives and tells Dexter that the Keeper has given instructions for all doses of the antidote to be moved to another location but when he removes them from the refrigerator, Will pulls out a gun. Over the intercom, the Keeper reveals that she gave him the weapon because she’s discovered there’s a sleeper among her own agents. Dexter insists he is innocent, but the Keeper orders Will to kill him anyway. A shot rings out and the scientists is killed. The Keeper doubted that he was the traitor, but she always felt he was too ambitious anyway. Now that Will has done what she asked, he wants to take the antidote out to the protestors, but the Keeper has just seen Sarah arrive on the security monitor and she wants her to have the decision whether the people outside should be allowed to live or die.

Sarah and Josh are becoming desperate as they try to find a way into the research centre. Josh starts to feel dizzy and has to sit down. Sarah’s phone rings and a voice on the end introduces herself as the Keeper of the Crimson Chapter. She offers Sarah a deal - her life in exchange for all those outside. One of her acolytes is coming to the door with syringes filled with the antidote and if Sarah accepts her terms, the protestors will be allowed to collect them. The Keeper points out that Sarah is already dying, so she has nothing to lose. She then delights in going through the symptoms those infected can expect in the new hour or so - their eyes will start to weep blood as their internal organs liquefy. Sarah agrees to come inside and the door opens - to reveal the acolyte is Will Sullivan. He wants to explain, but there isn’t time. She insists Will inject Josh with the antidote then together they can take the rest to the others. She tells Will that she’s glad they met and she asks him to give her love to Harry when he sees him.

Inside the centre, the Keeper welcomes Sarah at gunpoint to the Crimson Chapterhouse. Sarah wants to know why she’s condemning millions of people to die, but the Keeper points out the final death toll will be far greater than that as she has acolytes in cities around the globe waiting for her signal to release the virus. Sarah thinks she’s insane but the Keeper argues that she’s prepared to use any means necessary to fulfil their sacred prophecy, which makes her ruthless but not insane. Before she dies, the Keeper wanted to thank Sarah to her face!

Josh administers the injections to Maude while Will looks after Emily, but the younger girl is so weak they don’t know whether there’s still time to save her. They’ve now used up the last of the syringes and they don’t think it’s going to be enough so they decide to go back inside to see if they can find more. As they walk towards the building, Will asks Josh when exactly he was planning to kill him…

The Keeper wanted to thank Sarah because there were times when even she doubted the prophecies and her faith was tested - but all her doubts vanished when she learned of Sarah’s emergence. She’s proven that everything she ever believed is true. Sarah insists that she’s not the herald, but the Keeper says she has proof. They know that their alien benefactors last visited this world 500 years ago because the Book of Tomorrows was inspired by the journals of an Italian Duke who wrote of a young woman called Sarah who spoke of the future as though she knew it intimately. The mention of the name Guiliano sends a shiver down Sarah’s spine. It suddenly occurs to her that the building is owned by a company called Mandrake, which is the English equivalent of the word Mandragora, another name that’s mentioned repeatedly in Guiliano’s journals. All of this, the virus and everything the acolytes have done, was the result of something she said to Guiliano 500 years earlier. Sarah finally accepts that this is all her fault and she breaks down in tears…

Will realises that Sarah still doesn’t know about Josh being an agent for Sir Donald and the White Chapter. Josh denies it, but Will explains that he was told by the Keeper herself - and Josh suddenly realises that the Keeper is right here, in this building. Will pulls a gun on Josh and tells him he wants things to go back the way they were. Personally he never wanted to hurt anyone and was bullied and tricked into complying, but he accuses Josh of being a cold-blooded killer! Josh admits this, but says he was only protecting Sarah. He’s convinced that she’s the herald. She has to be…

The Keeper tells Sarah there were many within the Crimson Chapter who wanted her dead, but she wanted to be absolutely certain she was the herald before she had her killed. She hired Miss Winters to test her and once she was sure, she authorised Sarah’s execution - but thanks to her courage and several interventions by the White Chapter, she’s survived all their attempts to have her eliminated. Sarah is now feeling quite ill and is finding it difficult to concentrate. Before long, she loses control of her legs and collapses to the floor. The Keeper explains that after their last attempt to kill her in Antarctica failed, she realised the full significance of Sarah’s survival. The herald must not die until now, when the End Days are finally upon them! The Keeper assures her she’s not a monster and has no desire to see her suffer unnecessarily so she makes Sarah an offer - she can experience an excruciating death from the virus, or she’s prepared to end her pain with a single shot. Sarah has served her purpose now - in fact, she’s even flushed out the leader of the White Chapter for them. The Keeper asks Sarah for her decision…and she asks to be shot!

Josh asks Will to give him the gun, but Will warns him to stay back or he’ll shoot. Josh is convinced that Will isn’t capable of killing, but the doctor points out that although he may not have been a killer before he came here, he’s is now, as the death of Dexter demonstrates. Josh launches himself at Will and the two men struggle for control of the gun. Suddenly a shot is heard and a body falls to the ground.