Benson seeks Cassidy's help on a case in "Facing Demons."
Philip Winchester joined the cast as ADA Stone in season 19.
Dean Winters has appeared on SVU off and on since the beginning of the show.
In the 450th episode, a young man's suicide sparks a child molestation investigation.
Benson and Cassidy have a long history, but their romance soured in season 15.
Kelli Giddish joined the cast in season 13 as Detective Amanda Rollins.