The Cambridge University witches have been meeting for as long as the university has been around - over 900 years - they meet mainly to discuss books, though they do so on the roofs of the colleges and they drink hot chocolate while up there. The members are limited and selective, only those invited can join. In 2014 this includes Kat (a great spell-caster and professor of mathematics), George (a professor of Classics & all-round witch who seems to have no special skills), Amandine (retired French Literature professor and psychic, Kat's mother) and Noa (student of history - who sees people's secrets and can't help but say them).

Cosima, Kat's sister, is the chef/owner of Gustare, the best café in Cambridge, where they group meets every month. Cosima is also a witch and, when she begins casting spells to attract a mate (being desperate to conceive) everything starts to go wrong - she sets off a chain of events that turns each of the witches' worlds upside down.