The discovery of a mask in an ancient burial tomb in western Asia unleashes an alien force that could engulf pre-World War II Europe and the world in a genocidal holocaust.  When the Doctor, Val and Tom arrive in Venice in 1938, they stumble across the surviving members of the archaeological team that unearthed the mask.  Soon, they are caught up in a wild chase as darkness spreads across the city.  Can they survive a night that promises to spread its terrible darkness across the world?

The Vault - A secret Russian installation, dated back to the Second World War.  A research facility built deep into a mountain, dedicated to the collection and study of extra-terrestrial technology that crashes behind the Iron Curtain.  Even to the Russian government, it doesn't exist.  Its existence covered up since all contact was lost back in the 1970s.

On behalf of an old friend, the Doctor, Tom and Val accompany a UNIT research team to find the Vault and explore it.  What they find, deep underground, are the remnants of some of hte darkest days of the Cold War.  Secrets are revealed, crimes are uncovered.  Deep in the Vault, there is no way out and they are not alone and not all of their team are to be trusted.

Deep in the Vault, something is waking up. 

The Doctor thought he had everything under control.  The cell was constructed to his design: quartz-sapphire laser bars, stasis field, time loop - all set up within a reconstructed sector of the Time Lord's notorious prison planet of Shada.  He thought that would hold her.  But he was wrong - Bramahl has escaped and is out for blood.  Along with Tom and Val, the Doctor must track down Bramahl, and their only clue is her successor from Section 13 - Tamara Scott.  But her life as a companion was erased... wasn't it?  An old friend's timely return may hold the key.

Travelling back to a quiet English backwater at the turn of the twentieth century, the Doctor decides to give Val and Tom a taste of the paranormal when they visit Quarr Manor, the location of a mysterious fire which saw the Georgian mansion burnt to the ground with not a trace of a survivor to be found.

With just hours before the infamous fire is due to take place, the time travellers discover a sinister case of spontaneous human combustion in Quarr's rooftop observatory, sparking fears that a supernatural force is at work.  Soon a terrible dilemma faces the trio, as the Doctor begins to realise that Quarr's fiery visitant is just one of the dreadful effects of a terrible space accident, which threatens to unleash a firestorm across the whole of the British Isles.

Battling an anonymous threat which strikes without warning, the Doctor soon discovers that sometimes there is no good decision, as he faces the awful choice of sacrificing the few to save the many.

On the jungle world of Proteus, at the far edge of the galaxy, an archaeological expedition from the Hamilton Institute investigates an ancient tomb complex and its strange crystalline monument.  But the Doctor, Tom and Val discover that there are more secrets on Proteus than those buried in the ground.  What are the strange creatures that stalk the jungle after dark?  Why have seven members of the expedition gone missing?  And why can no one remember them?

As a devastating energy field begins to change the very world around them, Val and Tom become strangers to each other, and the Doctor uncovers a plot to steal the greatest prize of all.

This is the first part of two-part story

On the ocean world of Proteus, at the far edge of the galaxy, an archaeological expedition from the Hamilton Institute investigates an ancient tomb complex and its strange crystalline monument. But the Doctor, Tom and Val discover that there are more secrets on Proteus than those buried in the ground.  What are the creatures that stalk the shoreline after dark?  Why have seven members of the expeditiion gone missing?  And why can't the Doctor shake off the strange feeling that he's done all this before?

It seems that on this ancient world, the past has not been properly buried - and when the Doctor's own past starts to catch up with him, he begins to suspect that it's all a question of memory...

This is the concluding part of a two-part story

"There is something in the atmosphere above Earth.  You can't see it or feel it, but it is waiting, counting the days, the hours... waiting for Christmas..."

Professor Ruby Tranter was a senior scientist working for the grovernment finding new ways for mankind to survive in the 29th century.  Now they've retired her.  She feels cheated and bitter.  Her big regret is never having a child to love and which would inherhit her worlk.

Snow is falling inside the TARDIS.  The Doctor realizes someone is tampering with nature and sets off to stop them.

Using illegal government research, Ruby sets about making the perfect child in her laboratory and uses the snow to gather her data.  Next day the snowmen built by the local children come to live and envelop them.  The Doctor, Tom and Val must make Ruby stop her experiment so the real children can be freed.  But there is a further consequence to Ruby's experiment even the Doctor did not expect.