After a tough childhood and a few missteps, Thomas Sutpen finally establishes his dynasty by acquiring land, building Sutpen's Hundred, marrying Ellen Coldfield, and having two children with her. His "design," it seems, has come to fruition. Sounds pretty good.
Sutpen's son Henry brings home Sutpen's long-lost son, Charles Bon. Now there's a snag in the design because Charles Bon is part-black and wants to be acknowledged as part of the family. Oh, he's also in love with his half-sister, Judith. Sutpen does everything he can to prevent the marriage but ends up angering Henry, who repudiates his birthright and heads off with Charles Bon.
This is where things really take a turn for the worse. Charles Bon is dead (killed by Henry). Henry is who-knows-where. Sutpen tries to rebuild his empire but ends up offending everyone and getting himself murdered. And, to top it all off, Sutpen's mansion burns down. Looks like the design wasn't a success after all.