The CSI's investigate the brutal rape of a young girl, Robin Prescott, who was attacked while walking through Central Park at night, leaving her with no recollection of what happened. The semen collected off Robin does not contain DNA, the rapist was shooting "blanks", making it harder to link him to the crime. Danny discovers trace powder on Robin's dress is walnut dust used to clean statues and Stella tracks the dust to gardener, Billy Rendish, who was painting around the statues in Central Park. Billy's semen sample doesn't contain DNA but matching "nothing to nothing" is not enough evidence to convict him. Stella convinces Robin to try to identify her attacker in a lineup but when Robin doesn't show, Stella finds her dead in her bathtub, having slit her wrists. Stella goes back to the evidence and matches tree sap in the shape of a check mark on Robin's panties to a mirror image tree sap stain on Billy's jeans, proving Billy's guilt. Also, Mac and Aiden investigate the murder of drug dealer, Jordy Thompkins, who was shot in the abdomen, with the entrance wound frayed outward and the bullet missing. Bite marks on Jordy's body tell Mac and Aiden a rat ate the bullet. They follow a trail of rat hair/excrement/etc. to a deli/market, where Aiden uses a thermo alloy analyzer "gun" to find the now dead rat with the bullet inside its stomach. The bullet stria gets a hit in IBIS matching a gun used in a deli robbery one hour before Jordy was shot. Video surveillance leads them to drug user, Calvin Montgomery, who robbed the deli to buy drugs from Jordy. Calvin shot Jordy after he took Calvin's money, claiming Calvin owed him and refused to give him any drugs.