The story concerns the schemes of the orphan Jabez North to acquire an aristocratic fortune, and the efforts of Richard Marwood, aided by his friends, to prove his innocence in the murder of his uncle.

After a brief reconciliation, Richard leaves swiftly on the encouragement of Montague, who promises him help in turning around his hitherto dissolute lifestyle; on his train journey away from the town, however, he is apprehended by two detectives, Mr. Jinks and the mute Joseph Peters, who charge him with the murder of his uncle on the night of his departure.

Later encountering his twin brother, on his deathbed in a derelict neighborhood of Slopperton, he switches places with the dying man; after finding a body on the heath, the police declare Jabez North to have committed suicide.

With the assistance of the fortune-teller and chemist Laurent Blurosset and a mimic, Raymond manipulates Valerie into believing that Gaston has been unfaithful to her, and she poisons him for betraying her trust.

Valerie uncovers Raymond's plot, including the use of the mimic to trick her; when she confronts Laurent, however, he reveals that she did not in fact poison Gaston but merely drugged him—after the incident he fled Paris for a military life in India, and goes under the name of Captain Lansdown.

Valerie calls her uncle, the Marquis, to London; his paternal connection to Raymond is revealed when the pair confront one another, but the meeting is interrupted by an attempt to apprehend the latter (the evidence of his involvement in the murder having grown in the meantime).