The Companion is a short story, which was published by Titan Magazines in Stargate SG-1/Atlantis The Official Magazine 12.
Publishers Summary
The depths of Atlantis are explored - and a few surprises unearth for Rodney McKay!
Chronological Placement
The events depicted in this adventure are set sometime after Ronon Dex joined the Atlantis expedition, between season 2 or season 3 of Stargate Atlantis.
Extract
An official extract: