The Thorn features four of the band's album tracks recorded with orchestral instrumentation: "Overground" originally appeared on the Banshees' debut album The Scream; "Placebo Effect" was a song from their second album Join Hands, while "Voices" and "Red Over White" were previously released as B-sides of the "Hong Kong Garden" and "Israel" singles, respectively. The recording took place in Bavaria, in Germany.
The Thorn was released on 19 October 1984 by record label Polydor.
The purpose of the EP was three-fold: Siouxsie stated that she wanted to induct guitarist John Valentine Carruthers into the Banshees, to try out some string arrangements, and to simply re-record tracks that had evolved on tour. The songs from the EP were later included on the fourth disc of Downside Up, a collection of the band's B-sides.