In a vicious jungle landscape, a spaceship sits. It has been badly damaged in its crashlanding on the planet. The captain of the ship, Gordon Lowery, emerges from a gaping hole in the side of his ship. Both he and his shipmate, Marc Cory, seemed spooked by their ominous surroundings, although Cory seems to know more than Lowery about the real dangers here. Lowery senses this, beginning to regret the free-reign he has given Cory on the expedition thus far. He reports that there has been extensive internal damage in the ship. Even if he can repair it, he may not be done in time to make their escape rendezvous in orbit. Cory attempts to help in the repairs but his mind is obviously elsewhere. Both men await the return of the third crew member - Jeff Garvey - who should have returned long ago.

Little do they know that Garvey is in the jungle, not far from them, observing. He is still muttering his insane mantra: "must kill."

Lowery manages to extract one damaged part and sends Cory into the ship for a spare as he continues work. With his back turned, Lowery does not see Garvey move in on him from the jungle, murder in his eyes. Cory returns just as Garvey starts to lunge forward and fires his gun. Lowery watches in horror as his crewmate dies.

At first, Lowery is horrified at the seemingly-callous act. Enraged, he attacks Cory, but he is easily repelled. Cory examines Garvey's corpse and removes a small thorn which he handles carefully. He identifies it as a Varga thorn. That is what drove him mad and made him want to kill. Lowery doesn't understand but Cory dismisses him and helps the captain back into the ship, leaving Garvey's dead body on the jungle floor.

Unseen by both of them, the dead man stirs and sits up. His body begins to change. Bristly white hairs and Varga thorns grow from his skin. He is turning into a plant.

Inside the ship, Cory's demeanour changes and he decides to level with Lowery. He explains that he is a Space Security Service agent on a secret mission. He has a license to kill and the authority to enlist anyone (civilian or military) into service to help him if need be. Lowery has just been enlisted. Still angry over Garvey's death, Lowery insists on being given details of the mission.

Cory explains that the Daleks, who have not been active in the galaxy since their defeated invasion of Earth 1000 years ago, have continued their conquests in other places. In the last 500 years, they have gained control of over 100 different worlds outside of our galaxy. However, one week ago, a freighter pilot caught sight of a spaceship unknown in the galaxy. It was identified as a Dalek ship.

Outside, the mutating body of Jeff Garvey has come back to life. It struggles to stand.

Cory decides to try to contact their pickup freighter by radio. He tries for quite a while but does not get through. Likely a vital piece of the machinery has been damaged in the crash. On top of that, Lowery is now certain that he cannot repair the ship either. In his growing fear, he attempts to cast doubt on Cory's theory that the Daleks have established a base here on the planet Kembel, but Cory is more certain than ever owing to the presence of the Varga thorn. Varga are half-plant, half-animal creatures that only occur naturally in one place: the Daleks' home world of Skaro. The poison from the thorn infects animal life, replacing rational thought with the desire to kill and eventually transforming the animal into a cactus-like Varga. If the Varga are here, so are the Daleks.

Cory is right, the Daleks are on Kembel. In their control room, the black-cased Dalek Supreme enters and receives reports. Space monitor control reports that the emissaries from the planets will arrive on schedule and that "the conference" can begin at first sun. Security control reports that it has located the alien spacecraft and that a Dalek patrol will reach it shortly. The Dalek Supreme orders that the ship and its occupants be totally destroyed.

Later that evening, after night has fallen, Cory and Lowery work on a new plan. Lowery works to assemble a rescue beacon - a small rocket with message sending capability. They can record a message with their whereabouts and fire it into orbit with the rocket. Hopefully the freighter will get the message and come for them.

Cory watches the jungle warily. Varga plants have the capability of slow movement by dragging their roots. He has noticed three of them in the jungle around them. They are moving in. On top of that, he feels sure the Daleks know the ship is here. It is only a matter of time before they find it.

Again, Cory's instincts are right. The Dalek patrol's perceptors have located the ship. They split up in order to converge on its location.

Lowery, spooked by the relentless advance of the Vargas, tries to go after the plant creatures with his blaster at the ready, but Cory assures him they grow faster than he can kill them and urges him to continue work on the beacon. With luck, every listening post in the galaxy will receive their message once it is in orbit. But staying alive here until someone comes is another matter entirely.

As they work, a very large spaceship flies low overhead. Cory recognizes it as belonging to one of the outer galaxies. He realizes that whatever the Daleks are planning, it must be big.

At the Dalek HQ, two Daleks track the arrival of the spaceship. It is from Gearon, and it marks the beginning of the "Great Alliance".

With relief, Lowery finishes the repair work on the beacon. All they need to do is record the message and launch it. But before they can do so, Cory hears the sound of Daleks approaching. They grab the beacon and try to run. However, the Daleks burst into the clearing and they must conceal themselves in the underbrush nearby. They watch helplessly as the Daleks destroy the ship.

Using the distraction of the firing, Cory urges Lowery to run. The captain trips on the thick undergrowth and falls to the ground, accidentally pricking himself with a Varga thorn. He remembers clearly what Cory said would happen to him, but he pulls out the thorn and gets to his feet, running after Cory. The Daleks finish their work and move off in pursuit of the crew.

At the Dalek HQ, all of the seven delegates of the Great Alliance have arrived. They have convened in a large conference room, a strange group of creatures from the outer galaxies. The Daleks call the meeting to order, but one of the delegates, Malpha, objects. He tells the gathering that he has been informed that hostile aliens from the solar system are here on Kembel. This generates discontent among the other delegates. The Dalek Supreme admits that there are humans on the planet but that their spaceship has been destroyed and that they themselves will soon be found and exterminated. Malpha is still sceptical, worried that they may still be able to send a message to the solar system and inform them of the Alliance's plans. The Dalek Supreme assures them that if the Daleks do not kill the humans, the Varga plants will.

As Cory and Lowery hurry through the jungle, simply trying to stay alive long enough to get their message beacon launched, it looks like the Black Dalek may be right.

The Dalek conference moves forward and soon all the allies are agreed. They will all join forces together, with the Daleks in the lead. They will comprise the greatest war force ever assembled and their target will be the solar system. All of the planets will fall, and the first target will be Earth!

Cory and Lowery have found a safe hiding place for the moment. Cory is off on a short scouting trip. Lowery struggles against the Varga poison but is losing fast. His hand is already covered with the white bristles he saw on Garvey.

Cory returns and reports that he has found the Dalek city. He got close enough to overhear a message on the loudspeaker system there and has learned of the Dalek plan to invade and conquer the galaxy! In his haste to impart his information, Cory has not noticed the look which has come into Lowery's eyes. His mind has been taken over by the Varga plant. Suddenly, the murderous urge is upon him and starts to attack Cory. However, Cory is quick with his gun and kills Lowery. With no time to lose, he assembles the beacon equipment and records his message, telling the universe of the Daleks' evil plans and urging the receiver to get the information to Earth.

But Cory is too late. Just as he finishes the message, the Daleks discover him and burst into his hiding place. They do not hesitate a moment before firing. Cory falls dead, the recorder falling from his hand into the bushes. The Daleks do not see the recorder, satisfied that whatever he knew died with him. They depart for their city.