It began with her walking into the barn, the view over her shoulder the familiar interior with its inglenook fireplace, exposed stone walls and hammer beams. Sofas she’d once lounged on; tables where she’d discarded newspapers, eaten meals, set wine glasses down; hand-stitched wall hangings she’d marvelled at; and a sweater she’d seen her brother wear a dozen times, casually thrown over the back of a chair. There was a crumpled T-shirt on the floor near the dining table, where the remains of lunch still sat. And at the foot of the gallery stairs, two uniformed bobbies in their high-vis jackets, one looking appalled, the other embarrassed. Between them, a concertina of fabric that might have been a skirt. Disconcerting, but not terrifying. Because film couldn’t convey the stink of spilt blood.

But as Carol approached the wooden stairs, the camera panned back to reveal the ceiling above the sleeping gallery. It was like a Jackson Pollock painting whose sole palette was red. Blood; sprayed, slashed and streaked across the stark white plaster. She’d known then that it was going to be very, very bad.

The camera followed her up the steps, recording every stumbling step. The first thing she saw was their legs and feet, marbled with blood, drips and smears on the bed and the floor. She climbed higher and saw Michael and Lucy’s bloodless bodies marooned like pale islands in a sea of scarlet.

That was where the film froze, locked on that single terrible frame. But her brain didn’t stop running just because the film had. The blame circled and rattled in her head like a hamster on a wheel. If she’d been a better cop. If she’d taken matters into her own hands instead of relying on Tony to come up with answers. If she’d forewarned Michael that a man on the loose had his own twisted reasons to wreak vengeance on her. If, if, if.

But none of those things had happened. And so her brother and the woman he loved had been butchered in the barn they’d restored with their own labour. A place with walls three feet thick, where they had every right to feel safe. And nothing in her life was untainted by that single terrible event.

She’d always found much of her self-definition in her work. It was, she had thought, the best of her. A clear channel for her intelligence, it offered a place where her dogged determination was valued. Her ability to recall verbatim anything she’d heard had a practical application. And she’d discovered she had the knack of inspiring loyalty in the officers she worked with. Carol had taken pride in being a cop. And now she had cut herself adrift from all that.