The episode starts with a man going into a club, he seems in a good mood and tells the bartender that he has just made a deal of a lifetime. Then he looks around the room and spots an attractive lady smiling at him. He tells the bartender to pour the lady another drink and to put it on his tab. When the bartender turns her back he slips something into the women's drink.
The bartender then takes is over to the lady and the lady raises her glass at him in appreciation. Just as she is about to take a drink she looks in her glass and screams. The man at the bar starts to laugh, as he lights a cigar, then BOOM. The cigar blows up.
It then goes to a boy knocking at Danny's door saying "Hurry up we're going to be late." It is the neighbor's kid. Danny takes the neighborhood kid that morning to a church for the "blessing of the bikes," an annual gathering of New Yorkers who have their motorcycles, tricycles and such blessed.
On his way home the boy rides ahead of Danny, Danny runs to catch up with him. As Danny comes around the corner he hears a shot gun fired. He yells at the kid to ride home fast.
Then he sees the alleged attacker run across the road and into the subway. He has to make a decision to follow the attacker or help the lady in the grocery store who is screaming "help me, somebody help me!", holding a bleeding man in her lap. He calls in it on his cell and helps the women in the grocery store.
The episode leads to the team finding out that their childhood hero who was and still is a funny prankster in making funny pranks and toys for kids is still in business. And that the cigar came from him. They go to his store and the funny prankster finds everything funny and laughs at everything that they say. Flack then begins to get annoyed and says that they will arrest him if he doesn't take them seriously. The prankster sobers and does.
The episode ends with Danny having to go to his neighbor Rickki and tell her that her son, the neighborhood boy that Danny had taken out earlier with him, was dead. They both collapses in the hallway crying.
They finally find the killer of the explosive cigar only to find that it used to be one of the funny prankster'd child clients. They were only kids but they brought one of his products. A boat. They made it up and this man said that he his friend wanted to try it out first. So she hopped in the boat and he pushed her out into the lake. The boat began to sink and she couldn't get out. She drowned that day. The man had made a vow to himself that he would find this the funny prankster who created the toys for children and make sure that he would never laugh another day in his life.
He finally tracked down the prankster and makes a cigar with gunpowder in it. He then gave it to the prankster, posing as a happy client saying "thank you, we had a girl". But the prankster has just sold the business (to the man that you saw at the beginning of the episode at the bar) and to seal the deal hands the man the cigar that was just given to him.
As the man tells this story about his childhood and what had happened to his childhood best friend. The funny prankster is on the other side of the one way mirror looking into the interview room. And as the man tells the CSI about his vow, the funny prankster face shows expressions only of horror and remorse.