We knew, or at least thought we did, that John's brother Andrew had been killed by H.I.V.E., and discovered earlier this season that the reason was because he was involved in many of the same areas of crime they were, thus they eliminated the competition. It's a big twist, then, when it turns out that not only is he actually still alive, but is one of the Ghosts working for H.I.V.E. It's the main plot point of this episode, as they work on getting him back (even if John is reluctant), but it's not really cleared up how he came to work for H.I.V.E. in the first place. Presumably it began at the same time as he was announced dead, but was he just brainwashed by Darhk, or did he go willingly into the organisation?