"I think it was chiefly the death of his wife," said Colin. "Anyhow, he went all to pieces about two years ago, and ended up by getting run over in the Fulham Road. They brought him along to St. Christopher's, where we managed to patch him up. I felt sorry for the poor chap, and when he came out I got him that job at the Motor Club. As people go, I think he's by way of being rather grateful." He swung clear of the traffic outside the Ritz, and with a warning bark from the horn the little car leaped forward down the long, brilliantly lit slope. Turning up her coat collar with one hand, Nancy settled herself contentedly in her seat. "It's been a most exciting evening," she said. "I've enjoyed every single minute of it." "So have I," agreed Colin with enthusiasm. "What do you say to repeating the experiment next week?" "Only on one condition," replied Nancy. "I've got to take my turn in paying for dinner." "But that's absurd!" protested Colin. "I'm a great deal richer than you are." "No, you're not," was the indignant answer. "Why, I'm simply rolling in money. I've no expenses now except the rent of my studio, and Doctor Ashton pays me at least twice what I'm worth." "I don't believe that," said Colin. "Still, if you're determined to be proud and ostentatious I suppose you must have your way." He swerved to the left behind St. George's Hospital, and, cutting through the select precincts of Belgrave Square, came out within a few yards of the King's Road. In another minute they were turning the corner into Jubilee Place. "Next week's a bargain, then," said Colin, as they stood facing each other on the empty pavement. "It's no good trying to fix a day at present; I'll just ring up one morning and we'll arrange it over the 'phone." Nancy nodded. "That will be best," she said. "You mustn't desert the Professor--not unless he can manage all right without you." She gave him her hand, which Colin squeezed in a friendly grip. "Good-night, Nancy," he said. "Sleep well, and when you see Mark, tell him that for once in his life he actually prescribed the right treatment." He waited until the front door had closed behind her, and then, having lit himself a cigarette, climbed back into the car, and started off again in the direction of Campden Hill. It was a few minutes after midnight when he let himself in at the outer gate of the Red Lodge. The light was still burning in the hall, and, knowing from experience that the Professor frequently continued his work until the early hours of the morning, he walked straight through to the laboratory and tapped lightly on the door. As he half expected, there was a creak of footsteps inside, and the Professor himself, wearing an old Jaeger dressing gown, appeared on the threshold. At the same moment a peculiarly acrid and unpleasant smell drifted past him into the passage. "So you've come back, eh?" he said in his queer, high-pitched voice. "I hope you enjoyed your evening?"