Before I wrote my second, I knew that nothing but the death of Fraser-Freer would do me.

I recalled that Indian knife I had seen upon his desk, and from that moment he was doomed.

At that time I had no idea how I should solve the mystery.

But I had read and wondered at those four strange messages in the Mail, and I resolved that they must figure in the scheme of things.
The fourth letter presented difficulties until I returned from dinner that night and saw a taxi waiting before our quiet house.

Hence the visit of the woman with the lilac perfume.