Quicksilver

It's the telegram Constance never wanted to read:

DEEPLY REGRET TO INFORM YOU LT-CMDR H CLARKE LOST IN ACTION. CLASSIFIED OPERATIONS.

Those classified operations concerned a top-secret military project code-named "Quicksilver". A project based in Vienna. A project with alien connections.

But bombed-out Vienna is not what it was before the war – with its Strauss music, its glamour and easy charm. It's not the time nor the place for a happy reunion. As Constance Clarke is about to discover...

And as the Doctor is about to discover, too!