Bertrand is born on a Christmas Eve to a woman who had been molested by a priest.
She shares the last name of a family previously known to have produced a werewolf.
Bertrand grows up with strange sadistic and sexual desires which are usually expressed
as dreams. Sometimes the dreams are memories of actual experiences in which he had
transformed into a wolf.
His step-uncle, Aymar Galliez, who raises the boy (along with his mother and a servant),
soon finds out about Bertrand's affliction. Bertrand flees to Paris after an assault on a
prostitute, an incestuous union with his mother and a murder in their home village.
Aymar tries to find Bertrand by studying the details of local crimes, such as mauling of
corpses and various murders.
Bertrand joins the National Guard during the Franco-Prussian War, doing little fighting
and finding love from a girl who works at a canteen. However Bertrand and his love,
Sophie, are forced to deal with his affliction. They try to avoid the violent effects of his
transformation by cutting into parts of her body and allowing him to suck her blood.
Aymar finds Bertrand in Paris during the Paris Commune, but does nothing. Bertrand
is caught attacking a man after transforming into a wolf. Aymar supports burning Bertrand
at the stake, but a court trial sentences him to an infirmary.
Aymar transfers Bertrand to an asylum after the Versaillists have taken back Paris.
Unbeknownst to Aymar, Bertrand suffers in a small cell, drugged when he is visited by
his uncle. Bertrand eventually commits suicide by jumping from the building with a girl
he mistakenly believes is Sophie. Their deaths are similar to a suicide fantasy that Bertrand
and Sophie enjoyed; the real Sophie had previously committed suicide on her own, unable to
deal with her separation from Bertrand.