She watches you constantly.

Newly divorced Jo is delighted to move into her best friend's spare room almost rent-free. The high-tech luxury Camden flat is managed by a meticulous Home Assistant, called Electra, that takes care of the heating, the lights - and sometimes Jo even turns to her for Company.

She knows all your secrets.

Until, late one night, Electra says one sentence that rips Jo's fragile world in two: 'I know what you did.' And Jo is horrified. Because in her past she did do something terrible. Something unforgivable.

Now she wants to destroy you.

Only two other people in the whole world know Jo's secret. And they would never tell anyone. Would they? As a fierce winter brings London to a standstill, Jo begins to understand that the Assistant on the shelf doesn't just want to control Jo; it wants to destroy her.

'Chilling' Sunday Times. 'Brilliant! Horribly plausible' Reader's Digest.