Island of the Mad by Laurie R. King (2018)
Mary Russell and Sherlock Holmes travel to Fascist-controlled Venice to find a patient (Lady Beaconsfield) missing from the Hospital of St. Mary of Bethlehem (Bedlam). Mary finds it to be a great lark mingling with the idle rich on Lido beach while Sherlock takes a more serious slant to their search and considers the finer points to their investigation. Yet Mary prevails as Lady Beaconsfield and her nurse attendant also enjoy La Doce Vita and often venture from their island hideaway to join the gang at Lido. Mary concocts a clever scheme to rescue Lady B from her Fascist older brother who is more interested in the Lady's inheritance than her welfare.