FBI season 5 episode 17
Episode title: Imminent Threat (II)
To aid Scola in his undercover mission to find the terrorists believed to be behind the imminent attack in New York City, Maggie calls in Remy, whose well-connected informant from a prior case may be key to moving the operation forward. The crossover starts on FBI: International S02E16 Imminent Threat (I). It continues on FBI: Most Wanted S04E16 Imminent Threat (III).
