Alaide is brought to trial before the assembled judges, but concealed beneath a heavy veil. Osburgo testifies against her. When asked her name by the presiding Prior, she responds only with "La straniera". The Prior feels that he has heard her voice before, and he demands that she prove her innocence. She is reluctant to say much more. Suddenly, Arturo rushes in and proclaims her innocence and confesses his own guilt, stating that he killed someone whom he assumed was a rival. All appears to doom both Alaide and Arturo when, into the chamber Valdeburgo suddenly appears, announcing that Arturo is innocent and that it was in single combat with Arturo that he fell into the lake.