“There’s your tree, there’s mine. As long as you don’t move, there’s no chance of his seeing you. After he’s gone, don’t come out till I do. He won’t be here for a quarter of an hour or so, so don’t be impatient.”

“Righto,” whispered Bill.

Antony gave him a nod and a smile, and they walked off to their posts.

The minutes went by slowly. To Antony, lying hidden in the undergrowth at the foot of his tree, a new problem was presenting itself. Suppose Cayley had to make more than one journey that night? He might come back to find them in the boat; one of them, indeed, in the water. And if they decided to wait in hiding, on the chance of Cayley coming back again, what was the least time they could safely allow? Perhaps it would be better to go round to the front of the house and watch for his return there, the light in his bedroom, before conducting their experiments at the pond. But then they might miss his second visit in this way, if he made a second visit. It was difficult.