Adapted from the 1858 historical novel Le Bossu by Paul Féval, the film is about a skilled swordsman named Lagardère who is befriended by the Duke of Nevers.

With his dying breath, Nevers implores Lagardère to avenge him and his wife (who he believes was killed) and to look after their infant child.

Lagardère flees Caylus with the infant and finds refuge in the mountains in an abandoned farmhouse, where he discovers that the "son" is in fact a girl, who carries a locket naming her as Aurore.

Back in Nevers, after attending the funeral of her daughter — the coffin actually contains a wax doll — Blanche retires to a convent, and the evil Gonzague is named executor of her estate.

That night, the Regent Philippe d'Orléans arrives prepared to name Gonzague a royal agent to Louisiana.

The ceremony is interrupted, however, by Lagardère who escorts Aurore into the hall, introducing her as the majority holder of the Mississippi Company stock.

In his review in The New York Times, A. O. Scott described the film as "full of durable cinematic pleasures: a little sex, a lot of sword fighting and a plot that combines heady passion with complicated political intrigue.

"[4] In his review for Salon.com, Charles Taylor called On Guard "one of the best swashbucklers in movie history",[5] writing, "For sheer entertainment it puts nearly everything else that's playing to shame.

De Broca's film is a delight from top to bottom, packed with romance, adventure, beautifully executed swordplay and a sumptuous period look.

Auteuil's compact build and the precision he has always brought to his physical movements make him particularly suited to the elegant brio of fencing scenes.

Auteuil puts on a raspy voice; he walks through scenes stooped over and rolling his eyes so that you might almost believe you're looking at Groucho's French ancestor ...

[6]In his review on the What's on TV website, Jason Best writes, "As adroit and artful as his hero, de Broca gets the tone of Le Bossu perfectly right—romantic, thrilling and with a sense of fun that never slips into parody or self-mockery.