The episode begins with people reading the headlines that say that the mysterious disappearance of Tommy Lewis still haunts the neighborhood after twenty years. Monroe and Mac are discussing the case and Mac tells her that he was on the case and that time Tommy was eight. He then drives up to Tommy’s house. He tells her that Tommy’s parents had let him take the dog for a walk and that was the last they saw him. The owner of a shoe repair store was the first to see Tommy and he gave him a quarter to buy a lollipop from the store, the clerk at the candy store remembers Tommy buying the lollipop.
Mitch Ventri was the last person to see Tommy alive and the entire witness and tips boil down to Keith Milner, seventeen at that time and he used to be at the fire exit smoking dope. Four hours later, the people saw Milner in the park, holding Tommy’s dog and with Tommy’s blood on his jacket. He was high on angel-dust. By the time he was coherent enough to make a statement, his parents arrived with their lawyer and without a body and enough evidence, they couldn’t charge Tommy. And now Keith Milner is lying dead on the streets. Mac and Monroe arrive at the scene. Lovato states that Milner received a beating before his throat was cut.
And now the prime suspect from Tommy’s case is now killed exactly a block away from where the kid vanished and that too twenty years later, on the day Tommy disappeared. Looks like payback! At the lab, Monroe examines Milner’s coat. Next we see that Don is having a day off and he prepares breakfast and practices boxing with his old buddies. His grandmother calls him. In the morgue, Sid tells Jo that Milner was perfectly healthy and well nourished and he didn’t show signs of recent drug abuse. Guess he kicked the habit! Also, there is a single slash wound that cut the jugular and is the probable COD. Sid pulls out some substance from the wound which was transferred during the murder. But Milner was also attacked few hours before the murder and he was bruised; surprisingly there are no defense wounds.
Milner did not put up a fight with his attacker. Mac tells Danny that he always felt that it is not necessary that Milner was behind Tommy’s disappearance. The blood on the jacket could have been transferred from the dog as the dog too had blood on him. But back then no one considered young Mac’s opinion. Jo arrives and says declares that Nathan Lewis has disappeared. Well, Milner shows up on the twentieth anniversary of his kid’s death; Lewis does have motive! Later, Jo confronts Mac about the change in his work style and Mac doesn’t explain himself. Don is at his grandmother’s house, solving the mystery of her sink and opening jars. His sister arrives. At the office, Lewis’ wife tells Lovato that she thinks her husband killed Milner.
She then plays the last voice mail Lewis left for her where he tells her that he saw Milner and he sounded really upset. Hawkes tells Mac that the traces pulled out from the wound is from the green nettle plant and the ink on the jacket is used in printing press. Lewis did work at the printing press. Danny arrives and tells the team that Lewis’ cell phone signal hasn’t moved since they picked it up. The team arrives at the cemetery. They find Lewis drunk and passed out next to a grave. On waking up he asks the team is Milner is dead. Lewis says that he tried to kill Lewis. He is still not in his senses. At home, Don’s grandmother hands over his father’s stuff to Don and Sam, his sister does not anything that belonged to their father.
He finds a letter in a magazine that his father had written for him and Sam. He calls Sam and asks her to come over as there is something important that he wants to show her. During the interrogation, Lewis tells Mac and Monroe that he does not remember killing Milner as he blocked out. He tells them that Milner showed up in the bar and it took Milner a second to recognize him. He then left the bar and Lewis followed him. He then punched Milner several time s and Milner kept saying that he did not kill Tommy. He left him in that alley and the next thing he remembers is waking up on Tommy’s grave. Emma Milner arrives at the morgue to identify her husband’s body.
She tells them that Milner did not kill Tommy. Monroe wants to know what brought Milner to the neighborhood last night. Emma hands over Milner’s journal to Monroe. In the journal Milner has written that his parents went to their grave thinking that he killed Tommy and he feels that he deserves it as he stole money for drugs and now that he is going to become a father, he wants his son to look up to him with integrity and for that he needs to have a clear conscience. He wants to compel the guy who committed the crime to come forward and confess to his crime. This means Milner knew who killed Tommy. Next Jo meets Christine. She tells Christine that Mac might be struggling with something; like identifying objects etc.
Jo is worried and Christine tells her that she will keep an eye on Mac. At home, Sam reads the letter. Don tells her how much their father loved her and how he cried at her prom night when she wasn’t at the friend’s she was supposed to be at. And the next day morning when she returned, he was thankful that she was safe. Sam did not know any of this. She needs to get back to work and she leaves. At the office, Mac is struggling with identifying the shapes. Christine arrives and confronts him. She then asks him to identify what she has brought for lunch. Hawkes arrives and tells Mac that there is something important.
He says that green nettle and the other substances found in the particles from the wound have one thing in common, it is from a special Italian cheese and it is available at Ventri’s shop. Lovato and Monroe go to Ventri’s shop. He says he is sorry as he did some very terrible things. He admits that he took Tommy too the basement. He did not intend to hurt him but Tommy started to yell and he started beating Tommy. He never had touched a child before and after Tommy. He says that Milner had seen him but his parents did not believe him as he had several times for drugs and they were tired of their son. Then years later, Milner confronted him and wanted him to admit his crime to the Lewis.
Ventri did not know what to do and so he killed Milner. He tells them that Tommy is still in the basement. The team goes into the basement and finds Tommy’s dead body. Later, Mac tells Jo to be careful with where she sticks her nose. He asks her to stay out of his personal business. Mac goes to the Lewis’ and tells them that their son is found. Next, Don and Sam go to the baseball stadium where their father used to take them to see a match. Don looks at the urn in his hand and says: It is for you, Pop; and they run across the stadium with the urn in their hand. The episode ends.