Picking up where Scythe left off, Thunderhead returns to both Citra and Rowan as they find their places in a world that is shifting and changing for the first time in centuries. To this cast, the Thunderhead itself adds a third force - Grayson Toliver - an agent of its own with no access to its wisdom, but charged with helping it influence and protect those like Citra and Rowan who live outside of the Thunderhead's protective supervision.

As subtle and surprising as Scythe, Thunderhead extends the first book's examination of the human condition and begins to delve the philosophical vagaries of the interplay of near omnipotence with human emotion. Here, we enter the computer's mind, and the question that must be raised is this: Can a synthetic mind avoid the pitfalls of unbridled power?