It was love at first sight as only two writers could experience it. Andrea Cremer recalls that the YA novel she wrote with David Levithan, Invisibility (Philomel), which pubbed this month with a 125,000-copy print run, all began at ALA in Washington, D.C., in June 2010. “They put me—the newbie—on a panel with two god authors: John Green and David Levithan,” she says. Within minutes, Levithan was serenading Cremer in front of “a room full of 100 teenagers” with his rendition of the Righteous Brothers’ 1964 hit song, “You’ve Lost That Loving Feeling.” Levithan hastens to point out during the joint interview that he doesn’t do that “for just anyone.”

Reveling in the afterglow, Cremer subsequently wrote on her blog that, despite her being a YA author who writes novels about the paranormal and Levithan being a YA author whose novels emphasize popular culture and contemporary issues, he was her “writing soul mate.” She disclosed to her fans that one of her goals in life was to persuade Levithan to collaborate on a novel with her; she joked that they could call it Werewolf Bands of London.

The rest, as they say, is history: Levithan contacted Cremer and said, “Let’s do it.” The two wrote Invisibility in alternating chapters: Levithan wrote from the perspective of Stephen, a teenager who’s invisible to others because of a curse his grandfather, a powerful curse caster, placed on his mother before he was born, and Cremer wrote from the perspective of Elizabeth, a recent transplant to Manhattan from Minnesota, who can see Stephen. The two fall in love while trying to evade the curse casters and spell seekers bent on destroying them. It was a first time for both. Unlike Levithan, who has collaborated with John Green (Will Grayson, Will Grayson) and Rachel Cohn (Nick and Norah’s Infinite Playlist), Cremer, author of the Nightshade series, had never collaborated with another writer. She admits that she thought writing alternating chapters without outlining a plot together first would be “like writing a chain letter,” but Levithan advised her to think of him as her intended audience. Levithan, noting that he’d never entered the “paranormal-world-building-fantasy-curse-rules world before” says that the collaboration worked well “because each of us had an expertise we were bringing to the table.”

Today, Cremer and Levithan sign finished copies of Invisibility at Table 12 in the Autographing Area, 11:30 a.m.–12:30 p.m. And because they have “an open marriage,” Levithan jokes, each wrote on the side while writing Invisibility: Levithan’s Two Boys Kissing will be released in August by Knopf, and Cremer’s The Inventor’s Secret is due in spring 2014 from Philomel.