After casting Nathan Fillion’s new female partner, ABC’s straight-to-series light crime drama The Rookie has locked in a potential new love interest for the Castle alum. Dark Matter alumna Melissa O’Neil has been cast as one of the female leads in The Rookie, starring and executive produced by Castle alum Fillion.

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Written by former Castle executive producer/co-showrunner Alexi Hawley, The Rookie stars Fillion as John Nolan, the oldest rookie in the LAPD. At an age where most are at the peak of their career, Nolan cast aside his comfortable, small town life and moved to L.A. to pursue his dream of being a cop. Now, surrounded by rookies twenty years his junior, Nolan must navigate the dangerous, humorous and unpredictable world of a “young” cop, determined to make his second shot at life count.

O’Neil will play Lucy, a rookie cop in the LAPD who struggles with a domineering training officer and might be developing a budding romance with Nolan. She joins recently cast Eric Winter and Afton Williamson.

The Rookie hails from Mark Gordon/Entertainment One and ABC Studios. Fillion also executive produces with Hawley, Mark Gordon and Nicholas Pepper, Michelle Chapman, and Jon Steinberg.

O’Neil had a featured role as Two/Portia Lin on Dark Matter, which ran for three seasons on Syfy. She’ll also be seen in an upcoming arc on AT&T Audience Network’s praised conspiracy thriller series Condor. She’s repped by Adam Levine at Industry Entertainment and Daniel Birnbaum at Talent House.