On Quantico Season 3 Episode 4, Harry's approached by an FSB agent named Dmitri with intel that the Qumar emir is going to be assassinated. Harry's not exactly thrilled to see the guy who is responsible for his MI6 coworker's death, and he warns the team that Dmitri is not to be trusted.
The team decides to follow up on the threat in case it is legitimate. The emir is shot at an event, but it turns out that it is his son who is the real target. The emir was already dying from pancreatic cancer, and the prince is the next in line for the throne.
Alex and Mike stay with the prince as protection while the rest of the team tries to track down the Russian assassin.
Reluctantly, Harry works with Dmitri, and Dmitri is able to provide a way to track down Viggo, the assassin. Ryan realizes that Harry's coworker who died (Jeffrey) was also his boyfriend, and so that is why Harry is especially determined to kill Dmitri and is wary of trusting him.
The team uncovers that the prince's sister put out the hit on her brother, the prince, because she did not believe that he was worthy of the throne.
Meanwhile, Harry convinces Ryan to tell Shelby the truth, which goes about as well as you'd expect. Celine points out to Jocelyn that Owen likes her.