The riddle was solved the next morning.
Helen appeared at the office soon after nine and the moment she saw Mary she said, "Has Wally 'phoned you this morning?"
"No," said Mary.
Her cousin looked relieved.
"I want you to fib for me," she said. "You know the way the men stick together…. Well, the women have to do it, too…. At dinner yesterday," she continued, "Wally happened to ask me where I was going that evening, and I told him I was coming over to see you. And really, dear, I meant it at the time. Instead, a little crowd of us happened to get together and we went to the club.
"Well, that was all right. But it was nearly twelve when I got home, and he looked so miserable that I hated to tell him that I had been off enjoying myself, so I pretended I had been over to see you."
Mary blinked at the inference, but was too breathless, too alarmed to speak.
"He asked me if I got to your house early," resumed Helen, "and I said, 'Oh, about eight.' And then he said, 'What time did you leave Mary's?' and I said, 'Oh, about half-past eleven.'
"Of course, I thought everything was all right, but I could tell from something he said this morning that he didn't believe me. So if he calls you up, tell him that I was over at your house last night—will you?—there's a dear—"
"But I can't," said Mary, more breathless, more alarmed than ever. "Wally was over himself last night—and, oh, Helen, now I know! He was listening for your car every minute!"