Christmas Eve, 1892, and the falling snow is the stuff of fairytales. When the fairytale becomes a nightmare and a chilling menace threatens Earth, an unorthodox young governess, Clara, calls on the Doctor for help. But the Doctor is in mourning, reclusive and determined not to engage in the problems of the universe. As old friends return, will the Doctor really abandon humankind, or will he fight to save the world and Christmas from the icy clutches of this mysterious menace?
The episode is set in the Victorian era and sees the Doctor (Matt Smith) brooding with the assistance of Silurian Madame Vastra (Neve McIntosh), her wife Jenny Flint (Catrin Stewart) and Sontaran Strax (Dan Starkey), after the loss of companions Amy Pond and Rory Williams in the previous episode, “The Angels Take Manhattan”. He is forced out of hiding to investigate mysterious, sentient snowmen that are building themselves and meets Clara Oswald (Jenna-Louise Coleman), a governess also investigating the snowmen. They discover that the snowmen are being animated by the Great Intelligence (voice of Ian McKellen) with the help of a man named Dr Simeon (Richard E. Grant).
Building upon the character’s surprise introduction in “Asylum of the Daleks”, “The Snowmen” introduces Clara as the Doctor’s new companion, though ultimately it would be a third version of her character that would travel with the Doctor starting with “The Bells of Saint John”. In addition to Clara, “The Snowmen” also introduces a redesigned TARDIS, revised title sequence and theme music, and sees changes to the Doctor’s costume.