The Ox-Bow Incident is a Western which takes place 1885 and centers on Art Croft and Gil Carter, two cowboys. Art and Gil become a part of a band of men tracking down cattle thieves, along with Tetley, a former Confederate soldier, Tetley's son Gerald, and others. The novel takes a tragic turn when the group hangs three men found with cattle, only to find out later that the men had committed no crimes. Gerald and other members of the party are haunted by their refusal to listen to the men's claims of innocence.
Boasting the largest collection of book summaries, BookRags is the best option for titles you can't find elsewhere. They offer all of the basics (quotes, chapter summary, characters, historical context, literary criticism) but also walk through a few major topics that recur throughout the book, which can be particularly useful for essay writing.
The original provider of professionally-written study guides, Cliffs Notes were available in print form before the Internet even existed. Their content is very comprehensive and includes an analysis of characters, detailed chapter by chapter summaries, critical essays, essay topics, and many other sections.
Their book summaries aren't as good as other providers, but PinkMonkey often has interesting insights that aren't mentioned elsewhere on the Internet. For example, they go over literary elements (like setting, conflict, and mood), compare and contrast, and symbolism/motifs. It's a good site if you want to find a unique fact or angle that other students don't know about.