A remand prisoner is re-routed to a temp facility where she must play ball with her vile cellmate in order to identify her own unwitting connection to the terror attack that diverted her.

It seems like you are shutting the barn door after the horses have escaped.
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"In order to prevent a terrorist attack, an FBI agent goes to prison undercover and has forty-eight hours to deceive her cellmate into giving up the detail of the attack."
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It ups the ante if the Terrorist attack hasn't happened yet and getting the information from the cellmate is vital to stopping the terrorist plot.

Following a terror attack, a transiting prisoner is diverted to a detention centre where she must establish the unwitting nature of her connection to the attacker.

Is this about what would've happened, if Andy Dufresne got his chance at Elwood Blatch while still in Shawshank?
...forgive me but the wording seems confusing; what do you mean by "diverted"?