Carolina Castiglioni reached back to childhood memories of villeggiatura at Forte dei Marmi—the manicured Tuscan beach haven she’s frequented since cradle days—to give Plan C’s new collection a breeze of laid-back nostalgia. But don’t expect misty-eyed romanticism; her style skews boyish over frilly, grounded in functionality and sharpened with an artsy, utilitarian edge. “I wanted to go easy and pop,” she said.

Slouchy unisex pajama sets with contrast piping hinted at the de facto summer uniform of the Castiglionis. Whimsy tempered the practical: a crisp white poplin dress came low-waisted and puffed at the sleeves with a wink to rugby; a crinkled nylon anorak was elongated into a dress, and tossed over a lace-trimmed slip. A leather bomber leaned romantic, revealing a flower intarsia blooming at the back; a silky skirt suit was subtly padded to preserve its paper-doll silhouette, while tiny floral crowns danced across a billowing, transparent garden dress.

In a sweet nod to the raffia totes her grandmother once lugged to the beach, Castiglioni crafted petite crocheted pouches and baskets, while necklace pendants took the shape of toy sailboats and paddle boats—nautical memorabilia à la Plan C. On the same playful wavelength, T-shirts bore a painting of a flower vase she made, a teaser for an upcoming homeware collaboration with Belgian design label Serax. And there’s more on the horizon: with Plan C leveling up, the brand is setting down roots; its first Milan store is set to open soon.