The Doctor had heard about Cupid Flies time after time on Gallifrey, but never expected to see one in person, much less get bitten by one. The bug makes its victim fall completely in love with whatever other being it sees, and for the Doctor, this being just so happens to be Rose Marion Tyler. Will Rose be able to find a cure while resisting a Time Lord throwing himself at her?

The Doctor falls ill after a spider bite - and on boarding a medical ship after responding to a distress signal, learns he has been poisoned, and there is no known cure.. Ace decides to find the culprit and an antidote - but what she finds in the cargo hold is horrific - the Master is planning to wipe out the human race, and to ensure the Doctor dies with no hope of regeneration..