Radar Pictures has come onboard to produce horror-thriller “Spell,” from the writing team of Ari Margolis and James Morley III.Radar will produce with Dobre Films. “Spell” centers on a young couple who wake up with no memory of the first night of their tropical vacation. As they piece together the events of the night before, they discover they were the victims of a sadistic voodoo ritual, spurring a desperate quest for a cure for the horrific illness now afflicting them. Margolis and Morley have previously written and directed “Black Days,” nominated for the grand jury prize at Slamdance. They are currently attached to direct supernatural thriller “The Dead of Winter,” which they also wrote. The writers are repped by Dobre Films.