The Lost Ambassador by E. Phillips Oppenheim

Arrived in my room, I changed my dress-coat for a smoking-jacket, and my patent shoes for loose slippers. Then I suddenly discovered that I had no cigarettes. I glanced at the clock. It was only half-past ten. I had still half an hour to spare.

I locked up my room and descended by the lift to the entrance hall. My friend the hall-porter was standing behind his counter, doing nothing.