Doctor Miguel Azzini is found shot dead dead. The police suspect his colleagues: Elena Carli, his former mistress and owner of the clinic where he worked; Roberto Carli, her surgeon husband; Doctor Paula Lombardo, Roberto's mistress; and the clinic's administrator. Inspector Nardi discovers that Elena has a heart condition and had offered Miguel an increased sharehold in the clinic in order to dissuade him from leaving for another post. Elena's heart condition is worsened by the relentless police scrutiny and by her suspicion that Roberto is the murderer. She has to be rushed into hospital and is even more alarmed when Roberto prepares to operate...

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