It's the summer of 1939. London is on the brink of catastrophic war. Iris Hawkins, an ambitious young woman in the stuffy world of City finance, has a chance encounter with Geoff, a technical whizz at the BBC's nascent television unit.

What was supposed to be one night of abandon draws her instead into an adventure of otherworldly pursuit - into a reality where time bends, spirits can be summoned, and history hangs by a thread. Soon there are Nazi planes overhead. But Iris has more to contend with than the terrors of the Blitz. Over the rooftops of burning London, in the twisted passages between past and present, a fascist fanatic is travelling with a gun in her hand.

And only Iris can stop her from altering the course of history forever.