Richard Foreman/ABC
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Richard Castle and Kate Beckett (Nathan Fillion and Stana Katic), Castle
She's a steely NYPD homicide detective looking to solve her mother's murder; he's a mystery writer looking for inspiration. Castle's often-outrageous theories (time-travelling killers! Bigfoot!) help Beckett do her job. Outside the precinct, though, the two have built a relationship to rival the greatest love stories around.