Nash and Joe track their chief's murderer, who's involved in a billion-dollar money laundering scheme, and a turncoat federal agent to Las Vegas.  Cassidy proposes to Evan, and he accepts it, but while he's undercover, he was killed.  Nash breaks ther bad news to Cassidy, that Evan is dead.  Caitlin tells Nash her decision to leave the SIU and moves to Washington, D.C., where her sister just gave birth to a baby.