The flashback is a legitimate dramatic device, almost as old as the novel itself, and Hugo uses it here and in many other places in Les Misérables to good effect. To explain Javert's appearance immediately when he enters upon the scene would be to weaken all the dramatic effect of his irruption into Valjean and Cosette's peaceful life and would destroy the unity and steadily mounting suspense of the discovery-chase-escape sequence. As it is, crisis follows crisis until Valjean disappears over the convent wall; then, satisfied that he is safe, we are prepared to hear an explanation of Javert's presence.
The suspense in Chapter 8 is also very effectively maintained, and the working out of a complex criminal escape plot against the background of a convent also gives Hugo an opportunity for one of the dramatic contrasts both he and the reader enjoy.
