The Other Woman

Matlock agrees to defend psychiatrist Lucas Forbes when he's arrested for killing Adam Whitley, the husband of one of his patients whom Lucas was reportedly having an affair with, according to the woman's diary.

Matlock soon realises that Erin Whitley has a host of deep-rooted psychiatric problems. After a few chance meetings with a woman named Shannon, Matlock is shocked to realise the extent of the connection between Erin and Shannon.

A fairly involving episode finds Matlock taking on a case, which he admits during the trial as "a very difficult case he ever did", and there's a few twists, especially at the end. There are some implausibilities/unexplained bits and "Pseudo psychiatry science" but the story sucks you in with its acting and focus on the mystery at hand.