At a bowling tournament, professional bowler Chevy Cigs (who is up against Kyle "X" Chatts) starts to grab his ball but instead finds a disembodied head. Once Greg and Sara get to the scene, Brass ID's the victim as bowling alley employee Ronald Tobin. Tobin's girlfriend Shea also works at the ally. The detectives check behind the lanes to try to track down the body, but the only thing Greg finds is a bowling bag with some blood on it. Greg tells Nick his theory about how a head could get into the ball return zone. Since the pin settings are all automated now instead of manual, there are usually cameras to keep an eye on the pin mechanisms. There may be footage of the crime on the cameras. Nick checks Tobin's car and finds a homeless man sleeping inside. Vitas says that Tobin allowed him to sleep in his car and also got him a job at the bowling supply company.
Ray goes to a prison to investigate the apparent suicide of an inmate, Carla. Carla's attorney says that Carla always proclaimed her innocence for murder of her husband, James. Though she had prior experience with guns, she didn't have any gunpowder residue on her hands when she was brought in. James' sister, Hannah, was the one who called 911. However, Hannah wasn't named as a suspect due to her alibi: she was at the movies and had the ticket stub to prove it. The house was empty apart from the couple's 11 month old daughter. The jury didn't take very long to bring in a guilty verdict. And then Carla was found dead not long after. Ray compares photos of the hanging versus the scene of the murder of James.
Catherine checks over the victim's head. A box saw or a head saw was used to remove the head and the deed was done after Tobin was dead. A gunshot wound could have been responsible for some lung tissue that was found in the hose. Shea talks with Sara, and she confirms that Tobin and Vitas knew each other. Tobin wanted to become a pro bowler and actually managed to beat the X-man during a game. After running Chatts's prints, Sara discovers that he has had priors. Brass goes to talk with Chatts and says that his bowling bag was found with blood on it. But Chatts says that his bag was stolen during the first day of the bowling tourney. Brass then shows Chatts evidence that he and Tobin played a match: messages that people had written about the game in Twitter. Chatts agrees that he was upset, but that he couldn't be the culprit because he has an alibi.
Ray goes through Carla's case, trying to figure out what the circumstances were which caused Carla to hang herself. He discovers that a bullet could make the same entry wound path even coming from two completely different angles. Since it was a hollow point bullet, any sort of obstruction (like a windshield) would potentially change its trajectory.
Meanwhile, Greg and Nick go over the video footage from the pin-setter cameras. There is footage of the killer's hands, and also, there is footage from the previous night of Vitas lingering in the space behind the lanes. Brass takes Vitas in, and Catherine and Nick track down the murder weapon, along with a trail of blood which ends in a puddle of blood that has been cleared away. A bullet is embedded in the wall of the alley's garage. Eventually, they find the body hidden in a crate. On questioning, Vitas claims that he was behind the lanes that night to knock over pins for Tobin when he went up against Chatts. Vitas denies killing Tobin.
Ray takes Hodges to the crime scene to figure out where the bullet that killed James really went. Residue is found in the backyard, and they figure out that Hannah was the murderer, not Carla. Hannah, who now has custody of James' and Carla's daughter, is questioned. Ray reveals that they know she's the one who shot James and that they knew she didn't mean to frame Carla for the crime. Hannah says that James slept around and had three other children with three other women. He didn't deserve to live, but Hannah doesn't confess to the crime. Hannah is taken in and the daughter is brought to Child Protective Services.
The detectives go over the facts of the case. Both Vitas and Chatts were in front of the bowling lanes, and neither of them would have had the time to duck into the back and stick the head in the ball return before coming out again. So the team decides to test how long a ball takes to get returned. Greg deposits a test head behind the lanes and then tries to get to the front of the lanes. He manages it in 13 seconds. Meanwhile, Sara and Nick are going through the video footage of the tournament. Vitas and Chatts were pretty much at the lanes for the whole event, but Shea was darting through from the back. She gives the excuse that he was going to get her birth control pills. Catherine gives her her bag, which has been slashed upon. Shea says the bag was a present from Chevy.
Brass interrogates Chevy, and Chevy's apartment contains bullets similar to the one that killed Tobin. Shea fell in love with Tobin and it was all downhill for her relationship with Chevy after that. Shea stole the bullets from Chevy's apartment and killed Tobin, ready to frame Chevy for the deed. Catherine and Sara examine Chevy's belongings (his clothes and his bowling ball). Something about his version of events doesn't seem right. Tobin's blood is found in the holes of the bowling ball. There must have been some of that blood beneath the nails of the murderer. Chevy manages to win the tourney but he's arrested and taken away from the alley right afterwards.
Shea speaks with Sara, claiming that Tobin made her bring Chevy to the bowling ball warehouse, just to freak Chevy out a little. Tobin was shot by Chevy, and then he stuck the body in a crate. Shea retaliated for Chevy dumping her by cutting off Tobin's head and putting it in the ball return for Chevy to find. Later, the team bowls a game together.