While Judy sets out to find Grant Kelly, Penny and Will explore a mysterious tunnel. Light years away, Maureen, John and Don hunt for SAR's remains.

As the adults race to destroy all clues to the location of Alpha Centauri, the Robinson kids receive an ominous message from SAR.

The story of Don's run-in with SAR leads the Robinsons to an alarming realization. Will sneaks out on a dangerous solo mission.

As the battle for Alpha Centauri unfolds, the Robinsons and their friends risk everything to restore peace and pave the way for a better future.