Some readers and critics argue that the end of Act 3 in The Tempest is the climax of the play. At the end of Act 3, Ariel accuses Alonso, Sebastian, and Antonio of doing wrong against Prospero. Further, Prospero releases Ferdinand from his burdens of carrying logs and allows him to marry Miranda. If one considers the climax of a text the moment when resolutions begin to be made, then the end of Act 3 serves this purpose.
However, tension still mounts in the play through Act 4 as Prospero continues to seek retribution for having been usurped by his brother. It is not until the beginning of Act 5 that Prospero draws the magic circle and resolution really begins. In Act 5, Ferdinand is reunited with Alonso and the story makes a turn for the better.