Magnum, P.I. (1980)

When his friend Marcus is found dead on the beach the day after he's seen sporting an expensive new car he can't afford, Thomas suspects foul play in the demise of the former lifeguard and volleyball player. A young woman with an ambition to rise in the ranks of the police department joins Thomas in his investigation, and they uncover the married woman, the blackmail, and the fencing operation in the center of Marcus's secret life which led to his death.