Garro: Legion of One is the third audio drama for the Horus Heresy Series that was not originally released as part of an anthology or other release. Garro: Legion of One was released in both compact disc and MP3 formats and was written by James Swallow and performed by Toby Longworth. It was later re-released in an enhanced audio edition, but can still be bought as a stand-alone audio drama. This story, and all other Garro audio dramas and short stories were later published in printed form in the Garro main series anthology novel.