A magical production of Agostino Steffani’s Orlando generoso opened the 20thincarnation of the Boston Early Music Festival’s biannual exhibition and concert extravaganza on Sunday. Half barricaded by construction fencing on Tremont Street, the beautifully restored Cutler Emerson Majestic Theater offered an exquisite haven of disbelief for a tale of thwarted loves, mistaken identities, sudden transformations and, above all, human frailties.

Born in Castelfranco, near Venice, in 1654, Steffani spent most of his life in Germany, and died in Frankfurt in 1728. As a boy soprano he sang at major churches in Padua, Ferrara, and Vicenza, as well as in operas in Venice. Discovered and taken to Munich in 1667 by the Elector Ferdinand Maria of Bavaria, he sang in the court opera and was also provided with organ lessons. In 1672 he went to Rome to study composition, returning to Munich two years later and soon becoming known for his organ and harpsichord playing.