Summarize the masque Comus by John Milton.
With the official title of A Mask presented at Ludlow Castle 1634: on Michelmas night, before the right honorable John, Earl of Bridgewater, Viscount Brackley, Lord President of Wales, and one of His Majesty's most honorable privy council, but nicknamed Comus since then, was intended by Milton as an apologetic for chastity and purity. The storyline of the masque (an elaborate musical entertainment) is straightforward: Two brothers and their sister, designated simply as "Lady" become lost in the woods. While she rests, and while her brothers search for refreshment, Lady encounters Comus (in Greek Komos), the self-identified son of Bacchus and Circe - a liaison invented by Milton -, and the god of debauchery. Beguiled by his friendliness, Lady follows him, only to be captured and brought to his castle where, with the triple threat of a necromancer's wand, a magical cup and a feast of earthly delights, Comus lays siege to her chastity and purity, an attack which she stout-heartedly resists. Indeed, a large portion of the text of more than a thousand lines is made up of a philosophical debate on the merits of virginity. Eventually the brothers, led by the attendant spirit, Thyrsis, burst in. Comus escapes, leaving Lady magically bound to her chair. The attendant spirit solicits the naiad Sabrina who frees Lady by reason of her unconquered virtue. The three are then reunited with their parents, the whole masque concluding with the worthiness of innocence in this world and its triumph in the hereafter.