The TARDIS lands in the grounds of Newstead Abbey, Nottinghamshire, in 1850. Mistaken for a medic and his maid, the Doctor and Ann are brought to meet Ada Lovelace - the mother of computing and daughter of Lord Byron - who has recently fallen ill. But the travellers are not here by chance. Something odd is happening on Earth, and they’ve determined that this place is the centre of it. Strange figures are walking the land. Strange figures wearing bird-like masks. What do they want with Ada? And how will it change the future of humanity?