Ten years after Earth's electronics were fried by an immense solar flare, most human technology has turned useless; civilization has begun to fail. One thriving pocket is a valley on California's coast, where farmers in a religious cult dwell. A tribe of local hunters protect them. But this arrangement gets upended when a young refugee, Kyle Skander, wrecks his kayak there as he seeks to paddle north to his home. Kyle finds himself accused of murdering a young woman from the commune. To win freedom, he must find the real killer. His combative personality and a background in logic and philosophy helps Kyle make headway at this task. His investigation begins to uncover the valley's deepest secrets. Then, buried rivalries erupt into a battle that alters forever this enclave's fate. "Came A Horseman" re-imagines the Western as a post-apocalyptic adventure, with a murder mystery at the heart of its plot.