Compared to Reese, Dillinger's relationship with Finch was a bit more uncomfortable as Finch kept many more secrets from him (Dillinger was unaware of the Machine's existence during the time he and Finch worked together). While Dillinger used wit and humor with Finch more frequently than Reese, he was far more volatile and at times acted hostile towards numbers to get information. Nonetheless, he was skilled at his work, presumably having a Special Forces background and a long history of combat operations as he had a knife as a souvenir from Blackwater, one of the top private military companies. He demonstrated expert combat and marksmanship skills.
Dillinger's newest case was that of Daniel Casey, the Machine's latest number. Following a brief meeting with Lester Strickland, an associate of Casey's, Dillinger spotted Casey being watched by two people (actually Reese and Kara Stanton), who Finch identified as highly efficient members of the CIA. They placed a tracker on Casey and Dillinger followed his number to a bar where he met with a man going under an alias and claiming to work for the SSCI. Finch sent Dillinger a photograph of the actual man just as Casey tested the man he was talking to, confirming his suspicions that he was a fake.
Dillinger was meeting with Casey on the street when Reese and Stanton ambushed them; the man Casey met with at the bar opened fire at them, and was assisted by other men. Dillinger escaped with Casey while Reese and Stanton captured one of the shooters for information.
Dillinger decided that the Library was the safest place to bring Casey. Though Finch was uneasy with the decision, he and Casey began talking. Dillinger's hostile and aggressive attitude frustrated Finch, prompting him to tell Dillinger to keep on watch outside. Dillinger secretly planted a microphone to listen in on Finch and Casey's conversation.
Dillinger listened as Casey explained to Finch how he was a hacker for the government - he was hired to break into the Machine's code used a laptop to try and hack into it. He was able to acquire some source code and concluded his work when he was sedated and taken off in a car; the car crashed and Casey was able to escape with the laptop. Since then he had been on the run.
Dillinger came back in and took the laptop - since Finch had mentioned selling it, Dillinger learned that the Chinese were interested in buying it. He drugged Finch, rendering him unconscious, and told Casey to continue running.
Finch woke up and followed Dillinger to Central Park, where Dillinger decided not to shoot Finch and instead announced he was quitting. However, when Dillinger gave the laptop to his clients, he was shot in the chest. An ISA assassin arrived and shot at the men; one of them escaped with the laptop. The assassin revealed herself to be Sameen Shaw and shot Dillinger dead before leaving.