Gavroche, a streat urchin, got caught up in the movement of Revolution and went to the Rue Saint-Denis to help build a barracade to fight in the Revolution to defend his poverty. He was then sent by Enjolras to spy on the other streets.
Eponine went to the Rue Saint-Denis, both to help fight at the barracade and to be with Marius because she was in love with him. Eponine was killed putting a hand over a musket barrel aimed at Marius.
Jean Valjean went to the the barricades in the Rue Saint-Denis because Gavroche delivered to him and Cosette a letter written by Marius declairing his love for Cosette and explaining that their marriage was impossible because his grandfather would not give consent and stating that Marius was resigned to die. Jean Valjean went to the barricades to rescue Marius and bring him to Cossette