When a man collapses and dies in the middle of the annual San Gennaro festival in Little Italy, the team must investigate how the victim ended up with a wood sliver in his heart.

The San Gennaro festival draws over one million revelers annually, making the site a tough crime scene to process. When Stella and Danny are called to investigate a murder at this site, the clues lead them to a pool hall destroyed in a brawl. Meanwhile, Mac and Lindsay investigate the murder of a CFO found decapitated on a bench in Central Park. The investigation leads them to a financial office where the executives practice martial arts competitively. Also, Dr. Hawkes and Det. Flack investigate a suspicious apartment fire that kills a 10-year-old chess champion.