After crashing in 2020 London, the TARDIS crew has found the future of the universe altered and the human race doomed. As the Doctor tries desperately to unravel the paradox, all roads lead back to Baker Street, and the greatest test of all... 4.1 - Crossed Lines by Matt Fitton. The Doctor interrupts a pivotal journey for young Robin, while Tania and Helen are caught up in events past and present. As the timeline dissolves and the Void encroaches, the Doctor's friends ask the Curator for help. But he is not the man he was... 4.2 - Get Andy by Lisa McMullin. The Doctor resolves to make a difference and save one life in particular. But someone else is making a beeline for Sergeant Andy Davidson. Mr Bird has something to prove, and he will go to any extreme to do it... 4.3 - The Keys of Baker Street by Roy Gill. Homing in on the root of the problem, the Doctor attempts a risky solution - and disaster strikes. Soon, 107 Baker Street is all that's left of reality, as the residents climb the floors to face their destiny. 4.4 - Best Year Ever by John Dorney. What happens if the world is actually fixed? There are times when even the Doctor cannot help. And whatever the outcome, Liv and Tania have a decision to make. CAST: Paul McGann (The Doctor), Nicola Walker (Liv Chenka), Hattie Morahan (Helen Sinclair), Rebecca Root (Tania Bell), Tom Price (Sergeant Andy Davidson), Avita Jay (Zakia Akhtar), Colin Baker (The Curator), Jeremy Clyde (Tony), Alan Cox (Ken Bright), Joel James Davison (Robin Bright-Thompson), Clive Wood (Mr Bird), Amina Zia (Aisha Akhtar). Other parts played by members of the cast.