The Doctor has brought Donna to the twenties for a nice garden party. Meanwhile, a Professor Peach is murdered, in the library, with the lead pipe. Also at the party is Agatha Christie herself. Pity she won't remember it: the date is 8 December 1926, and Agatha will mysteriously vanish and turn up ten days later, confused and with no memory of where she'd been. Which means that whatever freaked out (not-yet-Dame) Agatha is about to happen. But right now, there's a murder to be solved! Also, Donna snogs the Doctor, but it makes sense in context and he tasted like anchovy.