CHILL FACTOR (paperback) by Christopher Knopf

Dr. Elinor Barry, a forensic therapist, has been summoned to evaluate the sanity of Dr. Frank Enari, one of two scientists assigned to work on a project involving monkeys at a high-altitude research lab isolated in an Arctic-like wasteland.  What they encounter is far more sinister and threatening than anticipated as they begin to suspect someone or something other than their research primates is inhabiting their polar station, driving Enari to an act Elinor must determine: criminality or insanity.