Now that Sam Baxter and the other forty million H2s-newly-evolved humans with different DNA-have revealed their presence to the world, their challenges have only begun. The rapidly-expanding network of H2s must address fears of their enhanced abilities, countering violent attacks even as they take action to address global crises of pollution and warfare. With the aid of the unique artificial intelligence, along with help from an unexpected quarter, humans tackle the challenges at "home" even as they receive a mysterious distress call from a distant planet.