Mom is behaving strangely-even for her, Will realizes, and the inquisitive teen can't rest until he discovers why. So begins a time travel adventure for Will and his sister, Halia-adventure Will has longed for but never thought possible, and that Hal would rather avoid. With the help of their next-door-neighbor and an unlikely feline ally (their cat, Chester), Will and Hal discover that their perpetually sunny mom is traveling back in time to relive her children's younger days and correct what she thinks has gone wrong in their lives. Even more incredibly, they find that Mom received the time travel technology from two aliens named Fost and Tuley. When a secret trip to the past goes awry, the teens discover that an unknown, malevolent actor is tampering with the timeline to corrupt the eco-friendly, technologically advanced future and that, unbeknownst to her, Will's mom has been given time travel to correct the events that will lead to those aberrations. After a series of plot twists involving a betrayal, altered DNA, role reversals, and memory wipes, Hal and Will find that their choices will help decide the path of the planet for centuries to come. Should they and their friends join the battle? Should they risk their safe, comfy today to fight for a better, greener tomorrow? Or should they be content in the security of the present and let the future take care of itself? How will the choices of a few regular kids (and their not-so-regular cat) affect the planet for ages to come?