The Langdon Codex

Two friends, one white, the other black, discover a solid silver lock-box hidden in an antique desk and, on impulse, one of them decides to steal it. Inside is a sheaf of papers bound with twine. Assuming the papers to be nothing more than a worthless diary, they toss them aside but soon discover their mistake. The manuscript is in fact a previously unknown sequel to Mark Twain's novel, Huckleberry Finn.
When the box is stolen, the men set out to find it and redeem themselves, encountering prejudice and bigotry along the way that parallels Twain's story, and leads them to a shocking truth about their own shared past.