Simon & Simon (1981) : 8x11

Woody Grant, John Channing, and Mark Fordham are all involved in an insider trading scheme using information gained from Woody's father's company. When Woody tells John he wants out, he ends up dead. His grieving father hires Rick and A.J. to investigate, and the two manage to finger John as the killer, but their mother's new beau Doug McKenna is an old Channing family friend, and ends up defending him in court, and in his attempt to defend a client he believes is innocent, he has to rip both A.J. and Rick apart on the stand. John is acquited of the crime, and the Simon brothers come under investigation. They manage to convince Lloyd Grant to keep them on the case, but they're going nowhere until Mark also tells John he wants out, and ends up being thrown off a walkway at the university library. They go to Doug with what they know, and the three hatch a plan to catch Channing at his own game.