What is the main conflict in The Mysteries of Udolpho by Ann Ward Radcliffe?

In the novel, Emily St. Albert is orphaned and left to the charge of her aunt whose new husband, Montoni, subjects both Mme. Cheron and Emily to cruelty in order to attain his mercenary ambitions. Confined to Montoni's castle di Udolpho, Emily witnesses many supernatural events. After escaping from Udolpho, Emily returns to France, where eventually all of the mysteries are explained and she is reunited with her love, Valancourt. The Mysteries of Udolpho is a truly engaging and compelling novel.