By the time Dan gets to the marathon, he is flat out, giving it everything he’s got. He sprints towards his future, the image of Atticus eating away the miles.

Luke and Dan finish hand in hand as the speaker calls out their numbers. They fall into one another, crying and laughing. When they look up, they see their family. Luke’s mum and Dan’s. Helen and Dave are holding a banner that says ‘Luke and Dan are Irons’. Dan’s mum is taking photos on her camera. When Dan and Luke approach, Helen drops the banner and pulls party poppers from her pocket. Their faces are coated with glitter.

But Atticus is missing. The adrenalin wears off and the cold sets in. Dan takes the foil blanket being offered, and the glucose drinks, but he doesn’t feel or taste them. Where is Atticus? Dan waits while the crowd thins. His family are impatient. They’ve been standing for hours and they want to go and have lunch. The table is booked.

‘Who are you looking for?’ Luke finally asks.

‘Atticus.’

‘Who?’

‘Atticus. My boyfriend.’

Dan doesn’t turn to look at Luke’s shocked face. Alarm bells are ringing. Atticus is not here. He didn’t reply to the text and he’s not here waiting.

Dan doesn’t even say goodbye to his family. A taxi would be quicker, his legs are shot. He’s running on empty, but his feet refuse to stop. They pound the pavement and Dan can feel that his socks are slick with blood. It makes no difference. He just has to get to Atticus. Dan takes the stairs to Atticus’s flat two at a time. He doesn’t knock. He uses the key Atticus hides under the doormat, fingers shaking in the lock, lungs screaming for oxygen.

Dan opens the door and solves the mystery. Who killed Atticus? It wasn’t Professor Plum in the bedroom with the candlestick. It was Atticus himself, with the hook that held a chandelier, in the living room with a rope. The first time Dan came here, he had wanted to be Sherlock Holmes and work out all the clues. Now he has. ‘When you have eliminated the impossible, whatever remains, however improbable, must be the truth.’

Dan collapses then, right under Atticus, whose feet swing above him. He’s wearing the pink loafers, which dangle dangerously from his bare feet. There is no danger any more, though. The worst thing that can happen in the whole world has happened. All Dan can do is lie down and weep.