Sir Gawain and the Green Knight is the story of the titular knight, a member of King Arthur's round table, who takes up the challenge of a stranger in green who rides into Camelot on New Year's Day. Gawain agrees to strike the stranger with his own axe, but with the understanding that the stranger will return the blow in a year and day. After the green knight suffers a mortal blow, he recovers unharmed. The story is richly allegorical and dwells on themes of Christianity and knightly valor.
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.
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From the creators of SparkNotes, this website tracks which chapters each theme and symbol appear in. You can also search for quotes by character or theme. Highly recommended if you are writing an essay on a particular theme or character.
This is a good choice if you're looking for a quick read or refresher rather than an in-depth analysis. You'll get a brief book summary and chapter by chapter breakdown. The website loads quickly with minimal advertising.