This is one of the weirder novels that I've read.

Spoiler

19 year old Pierre, engaged to marry 17 year old Lucy, comes across a young woman named Isabel who claims to be the illegitimate child of Pierre's father and a French refugee. To bring her better standing, he passes off as her husband and is disowned by his mother. The two of them, along with an abandoned servant named Dell, travel to New York to live with Pierre's cousin. Pierre's cousin denies them entry into the home and winds up marrying Pierre's fiancée. Lucy then comes to live with Pierre, Isabel, and Dell as Pierre tries to survive as a writer. Lucy's husband and her brother come to try to take Lucy back but are fought off by Pierre. Later, Pierre shoots Lucy's husband/his cousin dead in the street and is brought to prison. When Lucy and Isabel come to visit him, Isabel calls him her brother, and Lucy dies of shock. Pierre then takes poison and dies, followed a bit after by Isabel.

This has the potential to be a really compelling novel, but I don't love Melville's writing style here. At times, it's a bit difficult to follow and is a bit drier than other mid 19th century novels.