By the end of the week, life had become an intolerable dreariness, and to make matters worse, nothing was happening in the great world that called for Tab’s intervention and interest. He was in that condition of utter boredom when there happened the first of those remarkable incidents which, in his official account of the case, Inspector Carver refers to as “The Second Activity.” The flats, one of which Tab occupied, had originally been apartments in a private house. With little structural alterations they had been turned into self-contained suites. On each of the landings was a door of one of the four flats. Admission to the house was by the front door, and the landlord had so arranged matters that, whilst the key of each flat was different, all keys opened the street-door. It was, therefore, possible to go in and out without observation, unless by chance one of the other tenants happened to be on the stairs or in the passage-way at the time. On Saturday night Tab knew he would be alone in the house; the other three tenants invariably spent the week-end out of town. One was a middle-aged musician who lived on the top floor. Beneath him was a young couple engaged in literary work; then came Tab’s flat, and the ground floor suite was occupied by a man whose profession was unknown, but who was generally believed to be connected with an advertising agency. He was seldom at home, and Tab had only seen him once. The Saturday night happened to be the occasion of an annual dinner of his club, and Tab dressed and went out early, spent a mildly exhilarating evening and returned home at half-past twelve. There was nothing in first appearance to suggest that anything unusual had happened in his absence, except that the lights in his sitting-room were burning and he had switched them off before he went out. His first impression was that the waste of current was due to his own carelessness, but then he recalled very clearly that he had turned out the light and closed the sitting-room door before he went out. Now the sitting-room door was open, as also was the door of Rex’s old room. XVI