Assassins

Ashlyn is a lost kid, without a family, and without a home. At least, since her dad died.
S is a cocky, braniac rich kid, intent on solving cases to fill his time.
Kassidy is a scared little girl, terrified of what's waiting to come and get her.
A is S's best friend and willing to follow his best friend through thick and thin.
What happens when these unstoppable team meet each other and find a threat they might not be able to beat?