In this fabled 14th century poem, Sir Gawain takes up a Green Knight's challenge to strike him with an axe if the challenger will take a return blow in a year and a day. Sir Gawain accepts and cleaves off the Green Knight's head expecting him to die, but the Green Knight picks up his head and reminds Gawain to meet him in a year and a day, which he does and the adventure is only just beginning.
