Tom Winston (Cary Grant), a debonair Washington diplomat, struggles to raise three children by himself following the tragic death of his ex-wife. When beautiful Italian socialite Cinzia Zaccardi (Sophia Loren) befriends his youngest, most rebellious son Robert (Charles Herbert) then swiftly charms eldest David (Paul Peterson) and daughter Elizabeth (Mimi Gibson), Tom spies a quick-fix solution. He immediately hires Cinzia as a live-in nanny. Since Cinzia is looking to escape her stifling orchestral conductor father and meet a handsome man this situation suits her just fine, even though her domestic skills are next to nonexistent. Nonetheless when various mishaps force the family to relocate to a dilapidated houseboat on the river, warmhearted Cinzia helps heal the rift between Tom, a hitherto distant dad, and his unruly offspring. Inevitably romance sparks between Tom and Cinzia. However it happens Carolyn (Martha Hyer), Tom's newly divorced sister-in-law, has designs on him too.
While audiences were drawn to Houseboat by its charming love story, the clue to its true thematic preoccupation lies in its oddly haunting opening credits where lonely little Robert wanders in circles, forlornly playing his beloved harmonica. Hollywood in the Fifties was all about imbuing well worn genres like thrillers, westerns and dramas with new levels of psychological depth. In the case of Houseboat the same holds true for a family comedy. Interwoven with the deceptively lightweight, glamorous romance is a subtly nuanced psychological study of how children cope with bereavement and other life-altering changes. Between gags and flirtatious banter the plot spotlights how each of Tom's children deal with feelings of inferiority, insecurity and plain old fashioned fear. David takes to stealing things. Poor little Elizabeth yearns for a reassuring cuddle from her emotionally-distant dad. Robert is a handful and a half, if lovable with it. Tom is a classic Fifties male. You get the impression he would be more than capable at resolving any diplomatic disaster yet is convincingly clueless when it comes to family matters.
Naturally it falls to Cinzia to get buttoned-down Tom to finally loosen up and share some kind of meaningful dialogue with his kids. Which leads to one of the most disarmingly intelligent, nuanced and affecting philosophical discussions about death and moving on with life to be featured in Fifties family comedy. Interestingly Cinzia becomes this healing maternal figure without necessarily conforming to the oppressive ideal of a Fifties housewife. She can neither cook nor clean and proves fiery and outspoken rather than subdued by male archetypes. She is also flagrantly sensual and something of a hedonist, even self-centred in parts albeit conscious of hurting people's feelings. Indeed Cinzia's first interaction with Robert has her swipe a slice of pizza from him before instantly apologizing to the poor tyke. What Cinzia brings to the table is crucially: empathy, serving as the catalyst through which the Winston clan finally open up about their feelings. If the resolution to Houseboat's will-they-won't-they romance feels all but inevitable (how could they not? It's Cary Grant and Sophia Loren, for goodness sake!) the film, to its great credit, does not sugarcoat the children's reaction to having their hitherto lovable nanny transform into an unwelcome replacement for mom. Shavelson and Rose acknowledge there is work to do beyond the immediate fairy-tale ending. While undeniably episodic, Houseboat breezes along tremendous charm plus hidden depths beneath its frothy facade. Amidst an equally engaging soundtrack composed by George Dunning, the film includes songs performed by Sam Cooke and Sophia Loren, specifically 'Bing, Bang, Bong' one of her most fondly-remembered hits.