• falls exactly on a Doctor Who episode
• falls during the Classic era's season 3
• features the 1st Doctor (William Hartnell, 1963-66)

In the final days of Earth, the TARDIS lands on a massive spaceship carrying the last members of the human race to a new home beyond the solar system. The humans are not out of danger, however, as a deadly plague emerges from the most unlikely of sources: the common cold carried by the Doctor’s companion, Dodo.

Writer: Paul Erickson & Lesley Scott
Director: Michael Imison

More information at Wikipedia.