The window dressing of Julien Macdonald's business has moved way upmarket. Gainsbury & Whiting produce his show, George Cortina styles it, Charlotte Tilbury is in charge of maquillage, Steve Mackey's on the decks, et cetera, et cetera. But Macdonald himself brought things back down to earth with a cheerfully vulgar bump when he talked about the inspiration for his new collection. Jilly Cooper is the mistress of a literary medium known in England as "the bonk-buster," and it was her book Riders that turned Jools on for Fall 2010. The designer imagined a woman hot and bothered after a day on her horse, slipping into something sinful when she got home. So the collection breezily straddled two poles: sophisticated outerwear and suggestive, lingerie-influenced evening attire. The second outfit—a white, fur-trimmed parka with gray flannel jodhpurs—was followed by a rococo micro confection of flesh-toned chiffon and black lace.

And thus was the day-and-night rhythm of the presentation determined. The knits that first made Macdonald's reputation were skillfully represented here—on the one hand, by a substantial cable-stitched top, and on the other, by the merest suggestion of cobweb knit that wreathed one model's slender frame. There was a Ghesquière-esque touch in some of the short draped or plisséd dresses, but Macdonald carved out a new signature for himself with hybrid garments like a black leather biker jacket attached to a navy wool skirt, or a dress that featured the bottom half of a jacket bonded to a negligée top. It may sound a little unconvincing on paper, but on the catwalk, it certainly had the courage of its bonk-busting convictions. You can see why this kind of thing has courted a whole new client for Macdonald's fusion of hard and soft. And, hey, that same formula has sold millions for Jilly Cooper.