"Have you any special plans for this afternoon?" he asked. "If not, I thought I'd get on with that new parcel of stuff from Paris. The sooner it's sorted out and classified the better." The Professor, who was engaged in selecting a cigar, stopped in the middle of the operation. "Let me see, Gray," he observed, "how long have you been with me?" Colin reflected for a moment. "I came on a Wednesday," he said. "That will be three weeks to-morrow." "And I believe," continued the Professor, "that except for a few occasional pauses for sleep and refreshment, you have spent the whole of that period shut up in the laboratory." Colin gave a protesting laugh. "Well, I wanted to get the hang of things as soon as possible," he replied. "I can stand a lot of work provided it's interesting." "That appears to be the truth," admitted his employer. "All the same, every piece of machinery has its breaking-point, and, as I am beginning to find you extremely useful, I have no wish that you should suddenly collapse. You will therefore oblige me by going out into the open air and not showing your face inside this house again until bedtime." "Just as you please, sir," said Colin, pushing back his chair. "I suppose it would be no use my suggesting that you should try a little of the same prescription yourself?" The Professor shook his head. "I am more favourably situated than you, my young friend," he replied. "In the course of nature I shall soon have all the rest that I need." He chuckled at his own sombre jest, and, coming forward, laid his hand on Colin's shoulder. "You have been of very real assistance, to me, Gray," he added, "but there is no sense in flogging a willing horse. I can quite well spare you to-day, so off you go, whether you like it or not." Colin, who had been long enough at the Red Lodge to know the futility of arguing, at once rose to his feet. "I will see if I can rout out Mark Ashton," he said, "that doctor pal of mine I was telling you about the other day. I should think that with any luck we ought to be able to carry on until midnight." He accepted a cigar which the Professor offered him, and, making his way to the telephone in the hall, rang up the Shadwell surgery. "Hullo!" came a voice, "Who's that? Colin? Why, good Lord, man, we thought you were dead!" "Why should I be dead?" retorted Colin. "I'm not one of your patients." He heard a laugh at the other end of the wire. "As a matter of fact," he continued, "I'm just starting off to pay you a visit." "Splendid!" was the answer. "Mary's still away up North, but you'll find me here, and Miss Seymour, too. What more could you want?" "Nothing," assented Colin. "I was going to suggest that if you can get away this evening I should take you both out to a theatre." "No chance of that," replied Mark regretfully. "At least, not so far as I'm concerned. I might spare Miss Seymour if you'll do something for me on your way here." "What is it?"