Band leader and singer Danny O'Keefe, is drafted into the U.S. Army, along with three members of his orchestra, Chuck, Corny and Tiny, known as 'The Jesters.' Danny is unhappy because he has to leave the band's beautiful vocalist, Gloria Gold, behind. But he goes off happy since she promises be be true blue while he is serving his country. Danny spends every spare minute writing letters to Gloria, which she turns over to her elderly secretary to answer. Danny and his friends are stationed somewhere in Ireland. He is on guard duty when Molly Callahan comes driving up in a donkey cart, and he demands that she leave. She tells her father, Michael, who rounds up all the Callahan clan, and the result is that every American solder who looks at an Irish lass is beaten up. Danny's top-sergeant demands that Danny square himself and the other Americans with Molly and the Callahans, and he does so by the singing of Irish ballads. Molly falls in love with Danny, but Gloria shows up as part of a U.S.O tour.