Essex Palmer slips into a trendy New York nightclub to relax after a great day only to have his cigar blow up in his face, killing him instantly. Flack tells Stella and Lindsay that Essex was an internet entrepreneur, who made a fortune buying and selling comic bookstores and was fond of practical jokes. Essex's wallet is found near the entrance to the club, with prints on it from Mario Galanti. Flack arrests the man, but he swears he had nothing to do with Essex's death: he just took Essex's wallet--and dropped it after the explosion. Dr. Hammerback recovers part of the cigar from Essex's throat, and Lindsay has found DNA in a saliva stain on the man's tie from one Larry Gelatcher: Laughing Larry, a gag store owner who advertises his wares such as fake vomit and itching powder, in the back of comic books. After squirting Flack's tie with a fake camera, Larry tells the CSIs that Essex offered to buy his business, and he agreed. He gave Essex a cigar, but claims it wasn't one of his own--a stranger on the street who was celebrating the birth of a baby girl gave it to him. His "exploding cigars" don't match the one that killed Essex, so the CSIs suspect Larry was the intended target. They investigate one of his creditors, Kim Wey, but after literally chasing down Wey, it proves a dead end when the man claims he had no reason to kill Larry: he wanted his money, not Larry's death. Lindsay identifies the shop the cigar came from, and surveillance footage from the camera in the shop gives the CSIs enough to pull in several suspects for a line up. Larry recognizes the man who gave him the cigar: Benjamin Sudor. Benjamin tells the CSIs and Larry that one of Larry's gag items was responsible for his childhood best friend's death decades ago. After his marriage imploded, Sudor went after Larry, hoping the cigar would kill him.
Danny is awakened by his ten-year-old neighbor, Ruben Sandoval, who wants Danny to take him to church for the blessing of the bikes. Danny does, but on their way back, he hears a commotion from a robbery in progress and sends Ruben home. Danny hears a shot fired as he approaches the bodega, and sees a man run off, leaving the bodega owner, Justin Scott, badly beaten. His sister Lucy claims the robber fired at them, and both recall the robber had a blueish tint to the whites of his eyes. When Mac and Hawkes join Danny at the scene, Mac finds an orange with a bullet hole in it. Hawkes determines Justin was struck in the face with a revolver. Sid postulates that the bluish tint of the shooter's eyes might have been caused by a rare disease called Osteogenesis Imperfecta. As they're discussing the case, Danny is horrified to see a child's body wheeled into the morgue: Ruben Sandoval. Sid yells at Hawkes to get Danny out of the morgue, and Hawkes physically drags Danny away. Shocked, Danny tells Mac what happened and Mac consoles him, telling him he acted on instinct. Danny has the sad burden of telling Ruben's mother, Rikki, that her son is dead.
Citric acid on the bullet that killed Ruben connects his death to the bodega robbery, and Mac asks Adam to take over for Danny. Adam goes to Sid with a theory of his own: he suspects the eye discoloration was not Osteogenesis Imperfecta but rather the result of a unusual eyeball tattoo. Since there's only one tattoo parlor that does these kinds of tattoos, the CSIs easily zero in on Ollie Burns, one of the few people to get the special tattoo. Ollie admits to robbing the bodega but adamantly denies shooting Ruben; he claims he never fired his revolver and tells Mac where he can find the gun. The gun backs up Ollie's story; it doesn't match the bullet that killed Ruben. Mac uses a computer program to reenact the scene and determines that there's only one person who could have shot Ruben: Lucy Scott, Justin's sister. She's devastated when Mac shows her Ruben's body and tells her she killed an innocent child. Danny joins Rikki in church, but can't find the words to speak to her.