Det. Laura Murphy

Laura Murphy is a fresh detective transferred into the 15th squad, still finding her footing among veterans who don't hand out trust easily. She's earnest and eager to prove her instincts are sound, watching how the older cops work before she commits to a read of her own.

Somerville plays her without the swagger the squad room usually rewards, which makes her a useful outsider's eye late in the show's run — someone still learning the unwritten rules the audience has watched calcify over a decade. It's a quieter kind of newcomer performance, patient rather than showy.