|Portrayed by:||Bryan Dechart|
Aaron shows up as an arson investigator with Charlie McWenstle, wanting to question Vincent about an arsonist who has been setting fires around Manhattan. Trying to keep Vincent's identity a secret, Catherine Chandler and Gabriel Lowan stonewall both him & Charlie with their questions. Aaron becomes angry and starts lashing out until Charlie calms him down. Charlie then says how Aaron is a lot like the rest of his family, the Kellers. Catherine and Gabe then find out he is actually Vincent's nephew.
Vincent & Catherine later show up at the fire house, hoping to find out more information about the arsonist. Vincent is worried he'll be exposed, but Aaron doesn't recognize him as his uncle. Vincent helps Aaron & Charlie figure out the arsonist's next target, and Aaron tries to run off prematurely. Charlie, though, stops him. However, when they get word of a fire at the targeted building, Vincent & Catherine realize Aaron took off to confront the arsonist alone.
Aaron enters the building alone, and finds the arsonist, trying to shoot him. However, the arsonist gets the upper hand, and knocks Aaron out cold, leaving him to die in the burning building. Fortunately, Vincent goes looking for him and manages to save Aaron's life. Aaron begins to suspect there's more to Vincent than he lets on, but doesn't get a chance to question him. Catherine shoots the arsonist dead, and Aaron comes to her precinct to thank her. He mentions wanting to thank Vincent, but Catherine says he's undercover and she'll pass along the message.