If you haven't seen it, here's a short description:
When Ray and Fraser find out that some strange things are happening in a psychologic institution, Fraser decides to work undercover. Soon he discovers the dangerous secret: The doctors are testing a new medicine with the patients which causes depression. That's why five men committed suicide in the last few weeks. The institution tries to hush up this fact, and when they realize that Fraser and Ray are cops, their lives are in danger.
This episode belongs to my favourites of the first season, but there's one bad thing: I miss some more scenes for the psychiatrist and Walter. These characters could have shown us more feelings to understand the suicide-try of the psychiatrist and the confusion and desperation of Walter.
But this small "mistake" doesn't spoil the brilliance of this episode.