Boston is being terrorized by a series of seemingly random murders of women. Based on the true story, the film follows the investigators path through several leads before introducing the Strangler as a character. It is seen almost exclusively from the point of view of the investigators who have very few clues to build a case upon.

After forty years of good and faithful services, Robert T. Ironside, reprocessed police force of San Francisco, is finally on the point of tasting with the joys of a rest deserved well with Katherine, his wife, in their vineyard recently bought. However, a few days after his official departure, he is contacted by persons in charge for the police force of Denver, which offers the post of general manager temporarily to him their services, following the assassination for preceding occupying of the station in question. Initially reticent, Ironside ends up yielding and, with the agreement of his wife, agrees to take up the challenge, the more so as he has pleasure to find Susan, the girl of the one of her former assistants.