The garden gate of The Haven had opened and a man had emerged. There was no mistaking that tall, angular, straggling figure. It was Ian Murdoch, the mathematician. A moment later we confronted him upon the road.

“Hullo!” said Stackhurst. The man nodded, gave us a sideways glance from his curious dark eyes, and would have passed us, but his principal pulled him up.

“What were you doing there?” he asked.

Murdoch’s face flushed with anger. “I am your subordinate, sir, under your roof. I am not aware that I owe you any account of my private actions.”

Stackhurst’s nerves were near the surface after all he had endured. Otherwise, perhaps, he would have waited. Now he lost his temper completely.

“In the circumstances your answer is pure impertinence, Mr. Murdoch.”