See 'Castle's Nathan Fillion & Seamus Dever Reunite on 'The Rookie' (PHOTOS)

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SEAMUS DEVER
ABC/Eric McCandless
NATHAN FILLION, ALYSSA DIAZ
ABC/Eric McCandless

Nolan (Nathan Fillion) and Lopez (Alyssa Diaz)

NATHAN FILLION, ALYSSA DIAZ
ABC/Eric McCandless

Nolan and Lopez patrolling

THE ROOKIE
ABC/Eric McCandless

Suspicious behavior?

ALYSSA DIAZ, NATHAN FILLION
ABC/Eric McCandless

Something sure caught their attention.

NATHAN FILLION, ALYSSA DIAZ
ABC/Eric McCandless

Who’s in the car?

SEAMUS DEVER
ABC/Eric McCandless

Castle‘s Seamus Dever!

SEAMUS DEVER
ABC/Eric McCandless

What’s in the bag?

ALYSSA DIAZ
ABC/Eric McCandless

Why’d he just hand that over?

SEAMUS DEVER
ABC/Eric McCandless

His smile says he’s not worried.

SEAMUS DEVER
ABC/Eric McCandless

Ryan and Castle, together again!

SEAMUS DEVER, NATHAN FILLION
ABC/Eric McCandless

He looks mighty relaxed for a guy holding out his wrists for cuffs.

SEAMUS DEVER, NATHAN FILLION
ABC/Eric McCandless

Now he looks worried.

SEAMUS DEVER, NATHAN FILLION
ABC/Eric McCandless

Does Nolan now have the upper hand?

NATHAN FILLION, ALYSSA DIAZ, SEAMUS DEVER
ABC/Eric McCandless

Behind the scenes with Fillion, Diaz, and Dever

SEAMUS DEVER, NATHAN FILLION, ALYSSA DIAZ
ABC/Eric McCandless

Smile for the Castle reunion!

SEAMUS DEVER, NATHAN FILLION
ABC/Eric McCandless

Who’s arresting whom? Dever and Fillion have fun behind the scenes.

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As part of ABC's "Cast from the Past Week" in October, The Rookie's Nathan Fillion is getting a visit from two of his Castle costars.

Seamus Dever and Jon Huertas will be guest starring in the October 13 episode, "The Bet," and ABC released photos offering a look at the former's character interacting with Fillion's John Nolan. It looks like the former Detective Ryan may be on the wrong side of the law this time!

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'The Rookie's Nathan Fillion Fills in the Blanks on the Second Season

Find out what's next for his Officer John Nolan, details on that final cliffhanger, and more.

Also in this episode, Officer Nolan navigates building tension in his relationship with Jessica and a developing rapport with Grace as he works a high-stakes criminal case involving an undercover Homeland Security agent.

The Rookie, Season 2 Premiere, Sunday, September 29, 10/9c, ABC