Set on a near-future Earth and on the alien homeworld of S'hudon, Alien Day explores murderous sibling rivalries, old-school mercantile colonialism, ambition, greed, and the saving strength that can emerge from reluctant heroes called to do the right thing despite the odds.

Will Peter Holman rescue his sister Kait, or will she be the one to rescue him? Will Chloe Cary revive her acting career with the help of the princeling Treble, or will the insurgents take both their lives? Will Whistle or Twoclicks wind up in charge of Earth, and how will the Mother, who runs all of S'hudon, choose between them? And the most important question of all: who are the Old Ones that left all that technology behind for the S'hudonni … and what if they come back?