Jonas Fischer was a Chief Inspector of the FBI Office of Professional Responsibility. He was also a high-ranking mole for the Russians, using his authority to end investigations against the Russians that had gotten too close. He was killed by his prisoner Jane Doe.

Fischer arrived at the FBI New York office to interview Patterson regarding how much classified information she shared with her late boyfriend David Wagner. Assistant Director Bethany Mayfair immediately recognized that Fischer was targeting Patterson to further his own advancement and get Mayfair's job. Though Fischer told Patterson she was fired for getting David killed, Mayfair summoned Patterson to help Kurt Weller's team land a booby-trapped plane and thwart a terrorist plot. Mayfair then made it clear to Fischer that Patterson will remain with the FBI, to which he replied that she was engineering her own downfall.

When a Russian spy, whom Weller's team captured and turned on a previous case, is murdered by her own lawyer before she could name Fischer as a high-ranking mole in the FBI, Fischer returned to the New York office, claiming to be in the neighborhood to root out the spy, when in fact he was there to find someone frame in his place. He ultimately chose Jane Doe as his patsy, given that she had a flawed alibi for the night of Tom Carter's disappearance, and was able to cement his cause by subtly threatening an informant Allison Knight brought in, carefully making his comment seem directed at Patterson. Once the informant falsely identified Jane, Fischer took her into custody. However, just as Fischer had left, Weller uncovered his subterfuge by noting inconsistencies with Fischer's arrival, especially his comments on Turkish coffee, and got the informant to confess the truth. Weller's team pursued Fischer and managed to warn Jane that he was the mole. Fischer attempted to flee, but was killed by Jane.