Four hundred years ago, an expedition set forth from the Commonwealth of Humanity to colonize new worlds and expand the boundaries of human settlement. The expedition eventually settled four new planets—but never heard from the Commonwealth again. Now, facing a relentless and unstoppable enemy, the League of Four Worlds must attempt a daring mission to travel hundreds of light-years back to Commonwealth space for help. But does the Commonwealth exist, and if it does, will it be able to help?