Superintendent of St Agnes Asylum. Very much the country gentleman in tweeds and brogues, and obviously a pipe-smoker. Highsmith is a man of science (he's a member of the British Psycho-Analytical Society with a limited conversational range and no real interests outside his work (he is also unmarried).

Highsmith is one of the three men who signed Alexander Roby's commitment papers(the others being Doctor Lionel Trollope and Grahame Roby, and is the only one who seems keen to allow his release. He engaged Doctor Frederick Bartlett to consult on the matter and to make a recommendation either way.

He's coined the term 'Sympathetic Mania' to describe Roby's condition.