Mr. Trevor Bennett comes to Holmes with a most unusual problem. He is Professor Presbury's personal secretary, and until recently he has enjoyed the old Camford physiologist's implicit trust as though he were a close member of the family. The professor, however, has begun to act strangely after returning from a mysterious fortnight's absence. He is harboring an item that he is very aggressively protective over, and his behavior almost seems at times animalistic…can Holmes and Watson get to the bottom of what is happening?