After leaving a cryptic message with JJ, Spencer takes a few days off to go on an adventure of self-discovery. Aaron fears the worst and goes after him. Unbeknownst to them, someone else is following them and knows their every step, leaving behind a string of bodies. As Spencer and Aaron grow together, a pillar of darkness seeks to tear them apart. Will the BAU catch the stalker-turned-killer in time to save them both?