Prospero tells Ferdinand he was just testing him, "for I / Have given you here a third of mine own life" (IV.i.2-3) -- a puzzle for Shakespeareans but perhaps referring to one of de Vere's three daughters (Anderson 289). Ferdinand has passed the test, but he cannot consummate his relationship with Miranda until after the rites; he should speak with her (IV.i.32). Prospero has Ariel bring on a masque to celebrate the betrothal. If the play were only datable a couple years later than the bogus Stratfordian dating, this masque could be celebrating the marriage of James I's daughter Elizabeth, which took place in 1612 (Asimov 667). In formal, stilted verse, Iris, classical goddess of the rainbow, invites Ceres, goddess of agriculture, "A contract of true love to celebrate" (IV.i.84). Venus and Cupid, representative of the lustful side of love, are not invited (87ff). Juno and Ceres honor the couple and harvesters and nymphs dance. This kind of stylized court entertainment was for some reason popular in the early 17th century, however a big drag it seems to us (and undoubtedly to Shakespeare himself). Prospero the theatrical man emerges again in his identification of "Spirits, which by mine art / I have from their confines call'd to enact / My present fancies" (IV.i.120-122).
Prospero suddenly recalls that he's about to be murdered (!), so the masque mercifully ends. The couple remark on his mood, to which he replies,
Our revels now are ended. These our actorsThis passage is among the most famous of Shakespeare's and its significance transcends its context: an apology for aborting a masque and a contrast to the materialism in the following part of the scene. Oddly, it turns out "this powerful wizard pragmatically is a nihilist" (Bloom 681). It sounds to most like a statement made shortly before the end of the playwright's life (Ogburn and Ogburn 557) and is followed by a reference to "my infirmity" (IV.i.160) -- the same phrase used by Oxford in a letter of the 1590s (Ogburn and Ogburn 557-558).
Ariel tells Prospero he led the three conspirators into a "filthy-mantled pool" (IV.i.182). Prospero tells him to remain invisible and bring forth some gaudy apparel as bait for these thugs. He calls Caliban "A devil, a born devil, on whose nature / Nurture can never stick; on whom my pains, / Humanely taken, all, all lost, quite lost; /And as with age his body uglier grows, / So his mind cankers. I will plague them all, / Even to roaring" (IV.i.188-193).
Ariel hangs the "glistering apparel" on a lime tree and, while he and Prospero remain invisible, Stephano and Trinculo arrive, whining about how they smell like horse-piss (IV.i.199) and the liquor they lost (IV.i.208), with Caliban urging them on to the murder. Theirs will be the island "for ever, and I, thy Caliban, / For aye thy foot-licker" (IV.i.218-219). Caliban, generally speaking in verse here, calls the garish clothes "trash" (IV.i.224), but Stephano and Trinculo are dazzled by the "wardrobe" (IV.i.223) until spirits in the guise of dogs and hounds chase them all off, terrified. To Ariel, Prospero notes,
At this hour
Lies at my mercy all mine enemies.
Shortly shall all my labors end, and thou
Shalt have the air at freedom.