FBI Universe Crossovers: Revisiting The Franchise's Biggest Episodes Ever

"FBI" and "CIA" are kicking off new seasons October 5 with a pair of crossover episodes that will tee up the intricate, shadowy arcs to come. But if you're new to the franchise or are just now dipping your toes into its latest spin-off, "CIA," we've got you covered. 

Below, we're taking a trip through franchise history to revisit some of the biggest and most explosive crossover moments you may have missed. From the launching of multiple spin-offs to the "Imminent Threat" three-parter that had all our favorite agents teaming up, these episodes showcase the franchise's unique ability to share storylines and always raise the bar. In our list, we've included picks from all four series (including the dearly departed "FBI: Most Wanted" and "FBI: International"), all of which exemplify how these all-star installments continue to fuel one of the most action-packed and compelling worlds on television. 

Note: This is not a complete list of every "FBI" crossover ever, but rather a spotlight of some of the  most notable episodes that have blended its casts to tell bigger and badder stories than the average case of the week. Some of the episodes chosen include three-part stories that carry into other shows, while other picks feature well-timed guest spots that show how seamlessly characters can move between worlds in the CBS procedurals. 

Scroll down to see which memorable moments we've highlighted, then hit the comments to tell us which "FBI" crossovers are your favorites. (And if you're hungry for more, check out our behind-the-scenes deep-dive with showrunner Mike Weiss and the casts of "FBI" and "CIA," as they break down how these larger-than-life episodes get made.)  

Season 1 of "FBI" helped launch the franchise's first spin-off with a backdoor pilot aptly titled "Most Wanted." But the very next season, "FBI: Most Wanted" Supervisory Special Agent Jess LaCroix (played by Julian McMahon) headed back to 26 Fed to return the favor (and promote the new show, naturally). LaCroix resurfaced to help OA track down a suspect he arrested years ago after a school bus full of 26 children went missing. The Fugitive Taskforce head also brought members of his team including Kenny Crosby (Kellan Lutz), Sheryll Barnes (Roxy Sternberg), and Hana Gibson (Keisha Castle-Hughes) to help track down the abductor and assist with the case. The action then continued on "FBI: Most Wanted" (Season 1, Episode 9) as the collective task force helped track the terrorist's wife who was dead-set on carrying out her husband's deadly plans. It was one of the first times we saw multiple FBI teams come together for the greater good, but it certainly wasn't the last. Not by a long shot. 

Harking back to Dick Wolf's early days, the "FBI" crew even mingled with police from completely different cities and franchises. Such was the case in the Season 2 finale of "FBI" when they were visited by "Chicago P.D." Detective Hailey Upton (guest star Tracy Spiridakos) who temporarily joined the team as part of an interagency training program. In the episode, the FBI investigated the death of a college student after a drug deal went bad, only Upton quickly realized how her own policing methods clashed with the buttoned-up techniques of the FBI. The mini crossover mixed Wolf's #OneChicago world with New York's FBI, expanding both franchises' storytelling capabilities and serving as one hell of a sophomore season closer. 

Alana de la Garza brought Isobel Castille over to the "Most Wanted" spin-off whenever they needed the helping hand of the FBI's Special Agent in Charge. De la Garza was originally supposed to star in "Most Wanted," but plans changed when the character was brought on as a regular to the main series in Season 2. But that didn't stop her from crossing over multiple times throughout the spin-off's six seasons. She notably appeared again in a Season 3 episode titled "Decriminalized," which saw the team head to Vermont to track down illegal marijuana growers who may have killed some of their employees. But Isobel's frequent inclusion in the spin-off served as a concrete example of just how seamless the franchise's crossovers could be — and how solid its writing was throughout. 

The creation of the second spin-off "FBI: International" helped the franchise grow that much more with this first three-part crossover that began in the Season 4 premiere of the flagship series. It all began when a young woman was murdered on her way home from a yacht party. After a suspect was ID'd as a veteran with an Army connection to Crosby, Maggie called in her colleagues at "FBI: Most Wanted" to get to the bottom of it. Part 2 of the crossover event continued on "Most Wanted" during its Season 3 premiere, while the story concluded on the pilot episode of "International." 

In Part 3 (which kicked off the new spin-off and co-starred cast members from both "FBI" and "Most Wanted"), Isobel enlisted Special Agent Scott Forrester (Luke Kleintank) and his Fly Team to touch ground in Croatia to search for an American fugitive who escaped with a teenage girl. Zeeko Zaki's OA and Missy Peregrym's Maggie Bell continued working the case overseas. The three-parter was the biggest story the franchise had told up to that point, utilizing cast members and characters from all three Dick Wolf shows to help track the bad guys and save the day. (Also notable: This crossover marked the last appearances of Crosby after he was shot in the field. He survived the ordeal, but the character was then written off.) 

The third series in the franchise continued hosting "FBI" regulars during its freshman run. After a powerful pilot episode that hit the ground running, the show kept energy high with two guest-star appearances — Jeremy Sisto in Episode 2 and Alana de la Garza in Episode 3. In "The Edge," Jubal helped the Fly Team recover a child who was taken to Hungary by his young mom and later abducted. And in "Secrets as Weapons," Isobel was called on for help regarding a case about stolen cryptocurrency. Having "FBI" favorites on call helped validate the Fly Team's world and continued to help "International" stake a global claim and expand the franchise's boundaries. And incorporating even more familiar faces? Never hurts.

The cast of "FBI: Most Wanted" also lended a hand to help its sister series get off the ground. Julian McMahon's Jess LaCroix returned to the spin-off to help Episode 7's case of the week. After a founder of an illegal website was killed, the team was challenged to track down its co-founder in order to get to the bottom of the death. Even smaller appearances like McMahon's here continued to help establish the franchise's world of interlocking departments within the FBI's own rankings. And despite "International" taking place and filming in Europe (it primarily shot in Budapest, Hungary, but also rolled cameras in Croatia and Norway, among other locations), the series was still able to find clever ways to work in characters from other parts of the universe. 

Now in a groove, the three "FBI" series once again linked up for the three-part "Imminent Threat" story, which saw the teams unite to stop a potential threat brewing in New York City. Jubal Valentine (Jeremy Sisto) and Nina Chase (Shantel VanSanten) flew from 26 Fed to Italy to work with Forrester and the "International" team, combining forces to find a missing American whose disappearance was tied up in terrorists' plans. The story continued on "FBI" (Season 5, Episode 17) and wrapped up on "FBI: Most Wanted" (Season 4, Episode 16) where Maggie, OA, Scola, Nina, Jubal, Isobel, Forrester, Wallace, and more teamed up to stop the threat and save civilian lives. 

Not all guest spots dealt with an impending tragedy or terrorist activity. In Season 5 of "FBI: Most Wanted," viewers got up close and personal with Nina and Scola as they butted heads over the parenting style for their newborn baby. Shantel VanSanten was then a series regular on the spin-off, but this wasn't the only time their personal lives clashed with their professional ones. In Season 8, Nina returned to the OG "FBI" to finally marry her beau and baby-daddy, Mr. Stuart Scola — aww! (Read our post mortem with Boyd and VanSanten here.)

What happens when you pair an FBI agent with a member of the CIA? You get another "FBI" spin-off, of course! And the whole thing kicked off thanks to Jubal Valentine. The Assistant Special Agent in Charge was the man who originally paired Colin Glass (Tom Ellis) and Bill Goodman (Nick Gehlfuss) together, so naturally, Jeremy Strong was on hand in the pilot episode to link up the odd couple and get things going. The guest star would go on to appear in a total of six (out of 12) episodes of "CIA," helping cement the foundation of CBS' latest "FBI" series. 

When an international soccer match became the target of a bomb threat, Colin and Bill learned that the threat might be connected to two players who seemingly vanished into thin air. With a crunch for time, the team enlisted the help of "FBI" SAC Isobel Castille and field agent Maggie Bell, who suited up to help locate the girls' whereabouts and put the kibosh on those responsible. Once again, teamwork made the dream work!