And with a sweet, ingenuous smile Jimmy produced from his dressing-gown pocket a handful of biscuits.

There was a moment’s pause.

“And now I think I’ll toddle back to bed,” said Jimmy. “Night-night, Pongo.”

With an affectation of nonchalance, he mounted the staircase. Rupert Bateman followed him. At the doorway of his room, Jimmy paused as if to say good night once more.

“It’s an extraordinary thing about these biscuits,” said Mr. Bateman. “Do you mind if I just⁠—?”

“Certainly, laddie, look for yourself.”

Mr. Bateman strode across the room, opened the biscuit box and stared at its emptiness.