A Clue in Wax by Fred M. White

But it was anything rather than personal business that had induced Cheriton to turn his back on Seagrane Holt in the midst of that tragic crisis. At twelve o'clock the following day he found himself seeking admission to a flat in Gower-street and sending in his card, on which was pencilled a word or two, after which the man who answered the door informed him that Mr. Trevor Penton was at home and would be glad to see him.

Trevor Penton was a scientist whose knowledge of analysis had been more than once of considerable assistance to Scotland Yard. He belonged to the new school of chemists in criminology who can take a pinch of fluff found in a workman's coat pocket and resolve the mass into its component parts. He had been at school with Cheriton and they had kept up their friendship, more or less, ever since.