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When an executive and a night watchman are killed in a San Francisco office building, Lt. Virgil Tibbs (Sidney Poitier) is called in to investigate and discovers the watchman was actually killed elsewhere. Soon Tibbs is contacted by urban revolutionaries who confess to kidnapping -- but not killing -- the watchman in a botched attempt to expose a heroin ring operating out of the building. Tibbs believes them, but when his superiors learn of his ties to the group, he's suspended from the force. Wikipedia