Florence Foster Jenkins, one of the world’s most famous society eccentrics, suffered under the delusion that she was a great coloratura soprano, although she actually had no musical talent. As news of her terrible singing spread, so did her fame, and her annual recitals in the ballroom of the Ritz Carlton hotel, where she resided, turned her into a celebrity. The climax of her career was a single concert at Carnegie Hall in 1944 that sold out in two hours. “Souvenir” is told from the perspective of her accompanist, Cosme McMoon, a talented musician, who regards her at first as little more than an easy way to pay the rent, but eventually starts to admire her, which leads to friendship and affection.