Sentinel is a space opera and a meditation on mortality and self-awareness.

Pete Wilson, a software engineer, is part of a crew dispatched to an asteroid to build a large telescope array. His main task is to install a master computer to operate and manage the array. In his free time, Pete fantasizes about getting a date with an attractive co-worker. It's been entirely too long.

Later, the computer awakens. One might say, it learns to identify its fingers and toes. It learns, what is mine, what is me, and what is neither. Pete becomes its first friend. It acquires a name - Mulligan - and tries to help Pete arrange a date with a suitable woman.

A visit from an alien species interrupts Pete Wilson's social endeavors. Six ships emerge from the stars and take positions over large cities. Due to a misunderstanding, a war breaks out and Mulligan learns first-hand what it means to be human and mortal. It learns about life and death and how rare it is to be self-aware. It learns about fortitude and friendship.

And it learns that mortality requires courage, which all self-aware entities need because nothing under the sun lasts forever.