Twelve-year-old Virgo Capella is angry. He dislikes his stepfather, who projects his own childhood dreams of space travel on an unwilling Virgo. And he's stuck babysitting his bright, precocious little sister, Lyra.

While searching the local park for his lost pet snake, Virgo and Lyra encounter two odd street kids. Scorpio, a tough, guarded kid who's estranged from his father, and Biham, who looks like he just stepped off a spaceship. Lyra feels drawn to the strange and malnourished boy and cajoles Virgo to take him home. Scorpio tags along.

When a threatening cadre of ET...