It happened on Mardi Gras Day 2018. That’s when Michael Doucet, singer and fiddler in the Grammy-winning Cajun band BeauSoleil, met New Orleans singer-guitarist Sarah Quintana.

Living in the French Quarter at the time, Doucet was roaming through the Carnival madness with a large group including his guitarist brother, David. “People just got together and walked,” he remembered. “I didn’t know who they were because everybody was masked. It was a crazy, magic day. Things happened.”

When th...