For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Beowulf fights and defeats the demon Grendel.
Beowulf fights and defeats Grendel's mother.
Beowulf takes on his greatest challenge yet: a dragon.