"It's like a sirocco here," declared Royston Langdon, rock front man and Liv Tyler's other half, as he entered the sweltering Manhattan venue for the Hugo Boss and Interview Private Rooftop Concert: "I feel like Lawrence of Arabia." Like the British explorer, Royston and his bandmate brothers, Antony and Christian, along with drummer Jonny Cragg, were venturing into new territory. This was the former Spacehog crew's first gig as the newly christened Arckid.

In the audience, David Bowie nodded his head in approval and chatted with Interview's Ingrid Sischy. Royston's in-laws—Steven Tyler, Bebe Buell, and Todd Rundgren—watched with Liv, who looked remarkably cool in a white Zac Posen dress and black satin Dior heels. In this rock-star-studded family, has Royston taken the top spot? "I don't know about that," said clan patriarch Steven, with a loose-lipped laugh. "There's room for all of us."

After the 45-minute set ended, partygoers in the form of Julia Stiles, MTV's Damien Fahey, and a bevy of leggy, shorts-clad female fans spread out to enjoy garnish-it-yourself hot dogs, potato salad, and cold beer. "You guys were great. You look like you've been working together for a while," said one scenester. "Yeah, from the womb, really," retorted Royston. Ever the loving wife, Liv pronounced the evening's performance a success: "When you started," she said, "it was like you were playing for the whole city."