The senior prefects at Eton, known as ‘Pop’, were instantly recognisable, with their gaudy waistcoats and tightly rolled umbrellas. All the other boys in the school had to carry their umbrellas unrolled. But not today. On the Fourth of June all boys were allowed rolled umbrellas.

It wasn’t raining, so James had no use for an umbrella, and he wasn’t going to cart one around just for the privilege of having it rolled. He would buy a flower for his buttonhole, but that would be the extent of his showing off. He had no desire to ape the foppish dress of Pop.

He turned to Pritpal. ‘How do I look?’

‘Very grown up, I’m sure,’ said Pritpal, getting up from the chair. ‘Now, come along. Let us go and buy some flowers before they are all gone.’

There was one last thing and James would be ready.

He glanced sourly at his freshly cleaned top hat, sitting on his bed. How he hated that hat. He longed for the day when he could throw it in the bin and be done with it. But rules were rules.

He picked up the hat and they left.

Outside, they joined a mob of excited boys who were wandering down through town towards the river. On the Fourth of June the school was open to all, and the streets were already growing busy. Later they would be busier still, packed with parents, brothers and sisters, aunts and uncles, locals, sightseers, old boys and groups of newspaper photographers eager to get pictures of it all.

Eton was the most famous school in the country and many of the important men in England had studied here. King Henry VI had founded it nearly 500 years ago and since then it had built up countless bizarre traditions that were fascinating and baffling to outsiders. Most of them were bizarre and baffling to James as well, and he wondered if he would ever get the hang of the place.

But he felt carefree and relaxed today. It was a fine sunny morning and he was enjoying the holiday atmosphere. He had been tense ever since that night on the roofs and was at last beginning to unwind.

A pack of boys was clustered around an old woman with a stall selling flowers on Barnes Pool Bridge. James and Pritpal pushed in and James was just offering his money when he was grabbed from behind and pulled backwards. He spun round angrily and saw a wild-eyed boy whose blotchy face was streaked from crying. At first James didn’t recognise him.

‘Get off me, you idiot,’ he snapped, slapping the boy’s hands away.

‘I need the keys, James,’ said the boy, his voice strained, and at last James recognised him.

It was Mark Goodenough, the boy from the Danger Society who hadn’t made it the other night. The boy whose family was missing.

‘Oh, it’s you, Mark,’ said James. ‘Are you all right?’ he added, although he could see quite plainly that he wasn’t.