Episode 5 of "Memory of a Killer" begins with Angelo and Joe on a mission, as the former is transported back to his life five years ago. Angelo recalls being in Montana with his wife, Leah, as they make plans to move there and live the life they've always dreamed of. After their trip, Angelo and his brother, Michael, meet Dutch at his restaurant.
The brothers help Dutch cook, and Angelo notices that Michael's memory is starting to slip. Joe arrives, and Dutch mentions the dating app his nephew was developing, which had turned into a failure. Michael starts playing the piano outside, and Angelo checks up on him. He tells Michael that he's quitting their line of work and mentions that he'll let Dutch know soon. Michael warns that Dutch won't let Angelo go easily and reminds him about Don, another assassin who tried to quit.
Dutch's brother, JB, shows up at the restaurant and talks to Joe about Dutch. He warns Joe about the way Dutch treats the men who work for him. Later that night, Angelo talks to Dutch about his plans to quit. He reveals that he'll be moving to Texas, but Dutch asks him to come clean about what's happening. Angelo wants to stop and believes he deserves a break. Dutch initially agrees to let Angelo go but asks to speak to him about a mission. He asks Angelo to get rid of JB, whom he claims is stealing from him and using the money to shower women with gifts. Dutch is upset with his brother for stepping out of line and asks Angelo to finish one last mission for him.
After this, Dutch gets upset with Joe for not cleaning the dishes properly at the restaurant. Angelo goes to meet JB and talks to him about Dutch's orders. JB tells Angelo that Dutch is lying about him stealing. He reveals that it's Michael who is in charge of logging deposit slips after collecting payments from their clients. JB claims that Michael may have misplaced the slips due to his mental condition and asks Angelo to check with his brother.
Angelo is on his way to meet Michael when Leah calls him about their plan to move to Montana. At Michael's house, Angelo sees hundreds of sticky notes lying around with reminders that Michael has left for himself. He opens a drawer and finds the missing deposit slip that JB mentioned.
Angelo then encounters Michael outside their childhood home. The two brothers engage in a conversation about Michael's troubled state. Michael reveals to Angelo that he is experiencing memory loss and has been attempting to transfer Dutch's money from one account to another, but has lost track of it and doesn't know where it is. He expresses his fear that Dutch will kill him if he finds out about the money or his memory issues.
Meanwhile, Joe is frantically getting an employee to clean the kitchen before Dutch arrives, which only angers Dutch further, and he scolds Joe for not being able to follow instructions.
The next day, Angelo takes Michael to the hospital for a check-up. The doctor conducts a memory test on Michael and informs Angelo that he needs immediate help. Angelo brings Michael to his family home for the first time and introduces him to his wife and daughter.
Inside, Michael introduces himself to Leah as Angelo's work friend. In private, he advises Angelo to protect himself, Leah, and their daughter. He asks his brother to keep his condition a secret from everyone, including Dutch. Angelo promises to protect Michael from Dutch.
That night, Angelo visits Michael's office and removes all the sticky notes. Dutch requests Angelo to put a hold on JB's murder and tells him that he will be meeting with Michael to review the expense ledgers and account for the missing money.
Angelo informs Joe of this and asks him to investigate JB's ex-girlfriend, Kaleen. He calls Kaleen and gives her instructions on what to say to Joe in order to cause trouble for JB.
That night, Angelo sets up fake suitcases in JB's apartment to make it seem as if he is fleeing. Joe tells Dutch that JB is planning to flee, based on what Kaleen said, which makes Dutch believe JB has lied to her. JB tries to defend himself in front of Dutch, but Joe finds a bag full of cash there.
JB attempts to assign blame to Michael, but Dutch, in a fit of paranoia, orders Angelo to eliminate JB before their departure. In a grim act of betrayal, Angelo carries out the order in JB's apartment, while Dutch hands over JB's watch to Joe, heaping praise upon him for preventing JB from absconding with their funds. At JB's funeral, Dutch plays the part of a grieving brother, but later that night, he confronts Michael for his reckless handling of the accounting ledgers. Michael reveals that he's experiencing memory loss and struggling to keep up. Angelo implies that JB was taking advantage of Michael's condition. Dutch, seemingly moved by pity, urges Michael to seek the medical assistance he needs.
In private, Dutch expresses his concern that Michael might reveal details about their operations. He suggests eliminating Michael, but Angelo agrees to continue working for him if it means keeping Michael alive. Dutch offers to take Michael to a mental health facility that will provide care for him.
At the facility, Michael requests that Angelo step back and reminds him of their childhood when he killed their father to protect Michael. Michael confesses that he's afraid of Angelo before Dr. Jane escorts him to his room. That night, Angelo informs Leah that they won't be moving to Montana after all. The two argue, and Leah accuses him of hiding something from her for years.
The episode returns to the present as Angelo attempts to shoot his target through a window. He begins to experience flashbacks about killing JB, who had done nothing wrong. The episode concludes with Angelo in the car with Joe, where he makes a cryptic confession about killing JB to save Michael's life.
