Castle Episode 4.21 ‘Headhunters’ Promotional Photos, With Guest Star Adam Baldwin

CASTLE - "Headhunters" - With tensions rising between Castle and Beckett, Castle finds himself a new partner -- Detective Ethan Slaughter (guest star Adam Baldwin, "Firefly"), a tough and colorful cop from the city's gang unit. But Castle gets more than he bargained for when Slaughter shows him a grittier side of police work that puts Castle in the line of fire like never before, on "Castle," MONDAY, APRIL 16 (10:01-11:00 p.m., ET), on the ABC Television Network. (ABC/RANDY HOLMES)

ADAM BALDWIN, STEFAN NIEMCZYK (Photo by Randy Holmes/ © ABC)

STEFAN NIEMCZYK (Photo by Randy Holmes/ © ABC)

ADAM BALDWIN, NATHAN FILLION (Photo by Ron Tom/ © ABC)

NATHAN FILLION (Photo by Ron Tom/ © ABC)

STANA KATIC, SEAMUS DEVER (Photo by Ron Tom/ © ABC)

STANA KATIC, NATHAN FILLION (Photo by Ron Tom/ © ABC)

NATHAN FILLION, ADAM BALDWIN (Photo by Ron Tom/ © ABC)

NATHAN FILLION, JAN JANSSEN, ADAM BALDWIN (Photo by Ron Tom/ © ABC)

STANA KATIC, NATHAN FILLION (Photo by Randy Holmes/ © ABC)

SEAMUS DEVER, STANA KATIC (Photo by Randy Holmes/ © ABC)

ADAM BALDWIN (Photo by Randy Holmes/ © ABC)

ADAM BALDWIN, CHRISTOPHER RIVERA (Photo by Randy Holmes/ © ABC)

NATHAN FILLION, ADAM BALDWIN, CHRISTOPHER RIVERA (Photo by Randy Holmes/ © ABC)

JON HUERTAS (Photo by Randy Holmes/ © ABC)

CHRISTOPHER RIVERA (Photo by Randy Holmes/ © ABC)

CHRISTOPHER RIVERA, NATHAN FILLION, ADAM BALDWIN (Photo by Randy Holmes/ © ABC)

CHRISTOPHER RIVERA, NATHAN FILLION, ADAM BALDWIN (Photo by Randy Holmes/ © ABC)

NATHAN FILLION (Photo by Randy Holmes/ © ABC)

NATHAN FILLION, JON HUERTAS (Photo by Randy Holmes/ © ABC)

STEFAN NIEMCZYK, ADAM BALDWIN (Photo by Randy Holmes/ © ABC)

ADAM BALDWIN (Photo by Randy Holmes/ © ABC)

NATHAN FILLION, ADAM BALDWIN, STEFAN NIEMCZYK (Photo by Randy Holmes/ © ABC)

NATHAN FILLION, STEFAN NIEMCZYK, ADAM BALDWIN (Photo by Randy Holmes/ © ABC)

STANA KATIC (Photo by Randy Holmes/ © ABC)