EXCLUSIVE: Warner Bros has acquired screen rights to A Discovery of Witches, the bestselling novel by Deborah Harkness. Denise DiNovi and Allison Greenspan will produce. The debut novel is about a centuries-old vampire, a spellbound witch and a mysterious manuscript that draws them together. They’ll put a writer on it right away as the studio looks for more opportunities to tap the fantasy vein now that the Harry Potter series has concluded. In fact, the success of that final Potter installment has every studio foraging for the next young adult franchise. Harkness is writing this as a trilogy and the second installment, Shadow of Night, will be published by Viking next summer. Harkness was repped by CAA, which made the deal for the Frances Goldin Literary Agency.