"Darwin wanted to rid himself of his wife, Darwin knew she had written a love-letter, Darwin knew that Mr. Davies was in the house and would urge Mrs. Darwin to secure the epistle. Also the quarrel with Lee took on a new phase, a scheme for ridding himself of a pair of keen eyes.
"The only question to be solved was the one, Where was Darwin? Was he still in the city or had he left the country? I could not rid myself of the idea that Cunningham had some share in the affair. He was too keenly interested to be a mere on-looker. Could it be that Cunningham was Darwin, I asked myself. I investigated and discovered that the two men were never in the city at the same time, that they had never been seen together, although they were more than lawyer and client. The finding of the one hundred and fifty thousand dollars in Cunningham's strong box clinched the matter for me. I knew that Darwin was not likely to give another man the money which he would need himself with which to get away."
McKelvie paused and turned to me. "Do you remember the night he told us that pleasant fiction about the one hundred and fifty thousand dollars? I was positive then that he was Darwin, but I had no way of proving it and I had no desire to put him on his guard. That is why I advertised for Lee. I wanted to frighten him into thinking I was on to him and so catch him with the goods, which we were able to do, thanks to his own folly."
"And thanks to you, Mrs. Darwin's life has been saved," I said, as he ceased speaking. "I can never repay you for what you have done," and I held out my hand.
He grasped it with an embarrassed laugh. "Don't thank me. I enjoyed running him to earth. I'm glad he got his deserts."
"Did he really mean to kill himself?" I asked presently.
"No. I examined that closet. It had a double purpose. There was a trapdoor in the ceiling as well, and when you pressed a button in the wall a ladder was let down and you could escape over the roof. That was Darwin's plan, but in his haste he touched the wrong spring, for they were near together and it was dark, and so he fell to his death. Thus is evil punished in the end."
"How did Cunningham happen to have a sachet bag embroidered with his initials when Cora did not know him as Cunningham?" I inquired.
"He had foolishly preserved the one she had given him as Darwin. The initials on it were P. D."
"You told me that when I learned the answers to those questions that I should know who committed the crime. Why was it then that Jones and I did not guess the truth the night we heard Lee's story?"