American GI Ernie Williams, admittedly weak-kneed, has an uncanny resemblance to British Colonel MacKenzie. Williams, also a master of imitation and disguise, is asked to impersonate the Colonel, ostensibly to allow the Colonel to make a secret trip East. What Williams is not told is that the Colonel has recently been a target of assassins. After the Colonel's plane goes down, the plan changes and Williams maintains the disguise to confuse the Nazis about D-Day.

Dixieland cornetist Red Nichols runs into opposition to his sound, but breaks through to success. He marries a warm, patient woman and even finds time to raise a family. Then tragedy strikes when their daughter contracts polio.

Ventriloquist Jerry Morgan has failed with another love affair. The reason: when the relationship reaches the point when it is time to discuss marriage, his two dolls become mean and jealous. Morgan's dollmaker Papinek is a member of a spy ring who has stolen the secret plans for the top-secret Lafayette airplane. Since Morgan is leaving for Zurich the same night, he decides to hide the secret plan in the heads of the dolls.