The First Doctor arrives in Victorian London amid a Martian invasion. But he discovers all is not what it seems when Missy appears...

Soon, the Doctor is propelled into a future incarnation - the Tenth - but he is not alone in battling Missy and her Martian invaders. The Paternoster Gang - Madame Vastra, Jenny Flint and Strax - are also here to assist. But can they offer the Doctor any help in solving his own degeneration mystery?