Bloodline takes place during World War I. John Shaw, a nineteen-year-old, joins the British Army and is sent to the front lines, in the trenches.

Harker is famous for going on raids in the enemy trenches alone at night, and shows several feats of superhuman strength that seem impossible.

One night a soldier named Private Smith falls asleep on his watch, and Germans invade the trench.

As he passes out, he thinks he sees Harker closely inspecting a large gash in an enemy soldier's throat.

John soon becomes very sick with trench fever and believes he is having hallucinations of horrible things involving a hound and beheaded enemy soldiers in no man's land.

She reads his journal that he brought with him to the hospital, and learns about the strange and seemingly impossible feats Harker had done.

With Van Helsing's bag of vampire slaying tools, John and Mary follow Harker to Transylvania.

John and Lily's mother, Rosemary Shaw, who was believed to be dead, is also found living at the castle as a vampire.

It is all part of a master plan thought up by Tepes to raise the House of Dracula back to power with John and Quincey both united by Lily.

The day before their marriage, however, she kills herself by jumping out the castle window onto sharp rocks below because she was afraid of becoming a vampire, which was part of the master plan, and knew she would never stop loving Quincey, which would make it impossible to leave him.

The book ends with John remaining at Castle Dracula, Quincey going off to live somewhere else, and Mary and the baby, whom she names Grace, escaping back to England.