Special Agent Scott Forrester and his Budapest-based FBI fly team head to Croatia, after Isobel Castille enlists their help to capture an American fugitive who escaped to Zagreb with a 14-year-old girl. OA continues with the mission overseas, intent on bringing the fugitive to justice, while Europol agent Katrin Jaeger attempts to help the team secure the necessary support and access from the less-than-cooperative local authorities.

The crossover starts on FBI S04E01 All That Glitters (I) and FBI: Most Wanted S03E01 Exposed (II).

The International Fly Team is called on when a young mother flees to Hungary with her son, after losing partial custody of her son in the U.S. However, after the boy is kidnapped from his mother in broad daylight in Budapest, the team questions which parent is the danger in the child’s life

The team investigates when the hijacking of millions worth of cryptocurrency en route to a safety vault in Switzerland leaves an American transporter dead and another on the run.

The team investigates an American citizen who is proclaiming his innocence after seeking sanctuary at Madrid’s U.S. embassy while still covered in the blood of his murdered Spanish boyfriend. Also, Vo and Raines continue to grow their friendship.

The team investigates an American journalist’s death by poison after his attempt to meet with an anonymous source in Poland. Also, Kellett takes Forrester to task for being overprotective with her during the mission.

After a U.S. intelligence negotiator goes missing and her ransacked Paris apartment is discovered to be covered in her blood, the team is on the clock to find her before the country's nuclear secrets fall into the wrong hands. Also, Forrester finds himself drawing certain parallels to his mother's disappearance.

When an American founder of an illegal adults-only site is killed in Prague, the team is tasked to locate his co-founder, who is still on the run in Czech Republic; Kellett struggles to maintain a relationship with her mother.

When a group of Americans are among the victims of a bombing at a festival in Budapest, the team is brought in to find the perpetrators before they strike again. Also, when Vo's new beau is injured in the blast, she re-evaluates what dating truly means while in the bureau.

The team jets to Bulgaria when terrorists hold hostage for millions in cryptocurrency a concert hall filled with multinational student performers and their families. Raines is intent on proving his field skills, and Forrester receives news of their dog, Tank.

Kellett and the team reluctantly join an investigation in Northern Ireland, when one of Kellett's informants is arrested for his connection to a robbery and murder, and calls her to help clear his name.

When an NYPD officer is detained in Transnistria for aggravated assault, the fly team investigates his claims of infiltrating a sex trafficking ring being concealed by those in power; Forrester receives an unusual message from an unknown sender.

When a notorious American tech tycoon becomes involved in a murder in Frankfurt, Germany, the team must chase him down amid the local protesters he's incited with his conspiracy theories on social media.

A couple flees to Albania while awaiting sentencing for bilking millions in COVID-19 relief funds from the U.S. government; Kellett works the case from Budapest as she and Forrester try to regain their professional boundaries.

The team must figure out how to keep the U.S. attorney general safe amid a possible security breach while she's in Hungary for an important meeting.

When Raines' sister goes missing in Kosovo, he goes rogue to find her, putting his job and his life on the line; Kellett and Forrester face further scrutiny from inside the bureau.

The Fly Team lands in hot water when Vo is found at the scene where a Hungarian gambling regulator was murdered.

When an American vintner is shot and killed on his wine estate in France, the team must determine if the region's local protest group with a history of violence against foreigners is to blame.

Following a frenzied attack by gunmen aboard an American-owned river cruise ship on the Danube, the Fly Team heads to Vienna to investigate why the boat was targeted. Also, Forrester realizes his feelings of mistrust caused by his past are affecting his personal relationships.

The Fly Team and Jaeger head to Berlin when the 19-year-old son of an American billionaire is found unresponsive in his apartment. As the team works to determine if foul play was involved, they realize there’s a shadowy group on the case as well.

When a private jet carrying American citizens is shot down outside of a small town in Poland, the Fly Team looks into the man who missed the flight. Also, Forrester is conflicted when he receives information from his mother.