After spending years in the Peruvian jungle during his tour in Army Special Forces, Cascade PD Detective James Ellison developed hyperactive senses, which came back to him five years after his return to the US. He can see people in darkened windows at night from two hundred yards, hear the music playing on the radio of the car he's chasing after he's lost sight of it, and can distinguish between wood and plastic after both have been in a three thousand degree fire. Blair Sandburg, a local anthropology student, tells Ellison that he is a "Sentinel," who in ancient tribes would protect the village and seek out game using such hyperactive senses. Sandburg becomes Ellison's back-watcher and teacher of how to use his new powers as Ellison brings a whole new edge to the war on crime in Cascade, Washington.