Now Casey glanced at the intercom, and discounted it. There was an art to getting people to talk, but there was often a simple luck in getting to them in the first place. A phone could be put down in a second, the fragile connection cut so easily. Face to face was easier to assess, calculate, rush. Even if she hated it.

But how to get to him? Casey had tailgated dozens of people through apartment doors; it was the sort of illegality that rarely bothered the police. She had approached targets with any number of excuses. They all had, everywhere. Right the way up to the new Prime Minister’s wife, once, blinking on her doorstep in the dawn after an election. She had blearily signed for a big bunch of flowers, tugging her nightie to decency, glancing up too late at the wall of photographers. It had been worth a whip-round for that bouquet.

It was a beautiful day, the sky a scrubbed bright blue, spring rustling in the new green leaves.

Just then, Casey stiffened, hound to a scent. A blonde woman had walked out of the house, the slam of the door loud in the silent street. Her car keys in her hand, it was just a few steps to the Porsche, but the woman paused, glancing up at the sky.

Clio Greystone, Casey thought. The wife.

Casey assessed her dispassionately. Tall, with the same blonde hair Casey saw everywhere. A golden shimmer, with just enough expensive chestnut lowlights to avoid that hint of brass. Clio had an aquiline nose that a woman with slightly less confidence might have had tailored by some Harley Street artist. But it gave her face an elegance that was set off by a curving mouth.

She wore a beautifully cut blue dress, a leather jacket thrown over the top for the spring chill. Long legs ended in studded ankle boots, and Casey had seen Cressida carrying that bag last week. Balenciaga, at a guess.

A nice little trophy, she thought.

As Casey watched, Clio threw the keys back into her handbag and strode towards the gate. There was a bounce in her step, and the builders on the scaffolding opposite watched her appreciatively. A side gate purred open.

The Greystones’ road ended on a pretty high street, with several boutiques and a picture-perfect café that served cupcakes in a rainbow of colour. Casey followed Clio down the street, her mind racing. She walked past Ed and the security man, parked up, without a flicker.

At the café, Clio peered through a window, and a bell jangled as she pushed the door open.

Casey tapped at her phone. ‘Keep talking.’