The Shakespeare Code

As a reward for her help with the Plasmavore, Martha Jones gets a trip in the TARDIS. The Tenth Doctor takes her to 1599 England. After viewing a performance of Shakespeare's latest play, the time travellers are beset by apparent sorcery. Under threat of annihilation from a species from the Dark Times, the TARDIS team have to establish whether there is a connection between a witch they've met and Shakespeare's Love's Labour's Won — a play that was legendarily lost to time.