Frank Beardsley, a Navy Chief Warrant Officer, recently detached from the aircraft carrier USS Enterprise, is assigned as project officer for the Fresnel lens glide-slope indicator, or "meatball," destined to become standard equipment on all carriers. Helen North, a civilian nurse working in the dispensary at NAS Alameda, meets him first in the base commissary and again when Frank brings his distraught teenage daughter for treatment, where she explains that the young lady is simply growing up in a too-crowded house that lacks a mother's guidance. They immediately hit it off and begin to date, all the while keeping their mutual secrets: Frank has ten children and Helen has eight from previous marriages.
To spark a real romance, the wily Chief Warrant Officer Darrell Harrison arranges two almost comically mismatched blind dates. Helen is set up with an obstetrician who stands a good head shorter than her, and Frank is paired with a "hip" young woman who could hardly be more different from him. As a twist, Harrison schedules both dates at the same Japanese restaurant, hoping the setting will push them together.
After that successful dinner, the couple continues to date and eventually accepts an invitation to dine at Frank's home. The evening nearly derails when Mike Beardsley, Rusty Beardsley, and Greg Beardsley—Frank's three sons—secretly spike Helen's drink with gin, scotch and vodka, causing her to behave wildly. The moment Frank catches his sons laughing, he declares, > The court of inquiry is now in session!
Though the incident threatens the budding relationship, Frank proclaims his intention to marry Helen, adding, > And nobody put anything into my drink.
The couple then faces resistance from many of the children, who are wary of joining a blended family. Yet the 18 Beardsley offspring gradually come together, and Helen becomes pregnant. As they navigate these changes, Frank and Helen discuss cross-adopting each other's children, a plan complicated by name and lineage issues, including Philip North, whose teacher at the parochial school insists he keep his "legal" name—North—after his mother marries Beardsley.
Eventually, the birth of Joseph John Beardsley unites the children, who unanimously decide to be adopted under a single Beardsley surname. The eldest, Mike Beardsley, receives a draft notice and chooses to join the United States Marine Corps rather than take his chances. The film closes with Mike off to Camp Pendleton, signaling the blending of two families into one larger, enduring unit.
