The Ponce Massacre took place on March 21, 1937 in Ponce, Puerto Rico, when a peaceful civilian march turned into a police shooting. 19 civilians and two policemen were killed, with more than 200 others wounded. It remains the largest massacre in post-Spanish imperial history in Puerto Rico.

Professional gambler Dan Crown arrives in San Juan to visit his brother Alex, only to learn from the police that Alex has been found murdered. To Captain Acosta's questioning, Dan answers that he had no knowledge of his brother's affairs. Dan then finds Gina Rosario searching his hotel room, and together they begin to investigate Alex's death.