"Castle" Season 6 Episode 3, "Need to Know," ended on a note of Kate Beckett (Stana Katic) getting fired from her job at Attorney General's Office. Will this bring her back to the 12th Precinct and cut short her long-distance relationship with Castle (Nathan Fillion)? The preview of the new episode suggests that Kate is back in New York.

In the premiere episodes of the new season, Castle had 24 hours to live if the antidote to a stolen toxic chemical was not found. In the Episode 4 of "Castle" Season 5, "Number One Fan," Castle has only one shot as he has to deal with an unstable female who is his fan.

In the intense promo, an alleged culprit is holding hostages at gun point and wants to talk to Castle only. Emma Briggs (Alicia Lagano) is a murder suspect and wants Castle's help to prove her innocence. Billy Miller will guest star as Mickey Gerhardt, a banker at Wall Street who is sarcastic, hot-headed and one of the hostages. Castle gets caught in the hostage situation and his life is again at risk.

The sneak peek of "Number One Fan" provides a glimpse of the interaction between Castle and Emma. She is disturbed, unstable and is holding a gun. Castle has to prove her innocence to solve the hostage situation.

Castle is figuring out something via the text messages sent by her. In the sneak peek of "Number One Fan," he can be heard asking how Emma writes her text messages. Emma is telling him that she never spells out her words. In the last message, the word "love" has been spelled out, which Emma believes must have been sent by the killer.

"Killer used my phone ... you've to find the killer," Emma is telling Castle in the sneak peek of "Number One Fan." People who are held as hostage do not want Castle to leave them, but Emma asks Castle to go so that he can dust the phone for prints and find the killer.

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