Detective Inspector Carter is an inspector of New Scotland Yard. He is in charge of the case with the hiker and the backfiring car. He is warned (in a phone call) by Greg Lestrade to allow Sherlock Holmes five minutes on the crime scene, to listen to everything he says, and to try to not punch him in the face. At the time it is unfathomable, but DI Carter seems to come to an appreciation of its wisdom.