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.

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.

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.