Through her visions, a young book shop worker embarks on helping two police detectives catch a masked vigilante killing the men of a vicious career criminal, who killed her family. But is she friend or foe?

The question at the end of the logline should be removed, as the logline’s purpose is to describe a plot not tease per say.

Secondly the goal is confusing. Why does she want to catch the masked vigilante that’s killing the bad guys, wouldn’t she want to catch the killer who murdered her family instead?

The structure of the logline could be changed to emulate the plot of the story and add clarity, for example:

After a serial killer kills her family, a clairvoyant librarian must work with a police detective to catch the murderer.