Martin Ellis sits in his parked car at a motorway services, balancing a half-eaten burger over its paper wrapper. A cardboard cup of tea occupies the drinks holder beside a collection of fuel receipts.

His phone buzzes.

He glances at the screen, wipes his fingers on a napkin and answers.

"Martin Ellis."

He listens for a moment, then puts the burger back in its wrapper and reaches for the notebook on the passenger seat.

"Right. I was told someone might be getting in touch."

He finds a pen beneath a folded road atlas.

"Go on, then. What's happened?"