NBC has released an official description for the April 20 episode of Grimm which features guest star Sebastian Roche (The Vampire Diaries). The episode is called "Cat And Mouse." Here it is, complete with new spoilers:
NICK MUST CHOOSE SIDES WHEN HIS DUTY AS A GRIMM CONFLICTS WITH HIS DUTY AS A DETECTIVE -- BREE TURNER, SEBASTIAN ROCHE AND NEIL HOPKINS GUEST STAR - While investigating a string of murders, Nick (David Giuntoli) and Hank (Russell Hornsby) learn that their suspect's crime wave began overseas. When Nick discovers the suspect (guest star Neil Hopkins) is being harbored by none other than Monroe (Silas Weir Mitchell) and Rosalee (guest star Bree Turner), he realizes he's hunting the hunted, a freedom fighter trying desperately to escape the clutches of a creature bounty hunter (guest star Sebastian Roche). Bitsie Tulloch, Sasha Roiz and Reggie Lee also star.