The summary is in the story

This new guardian is the spirt of Halloween, but is kinda like a ninja. She gets kidnapped by the guardians, says no to their offer of becoming like them, and more things will happen in the story. Description isn't that good, but story will be better.

Aria Jones has been hurt by the very same species that she is about to encounter; werewolves. She has a major eating disorder and feels unwanted in the world. Her mom finds her laying unconscious in the living room and no sooner, they are both packing up to leave this town and onto Beacon Hills. Scott Mccall takes an interest in her and tries to know her. Takes place in season 3.

What is Tris never chose Dauntless and stayed in Abnegation? Read to find out more. This is a oneshot kind of thing.