James Mayer was an alien from another dimension who had integrated himself into the Torchwood team. To further understand the flotsam and jetsam that fell through their version of The Rift, the Border Princes fully integrated themselves into their host dimension to the point they fully believed they belonged there. Fail-safe were in place to remind them of their true nature in case of damage or other failure. This failed with James which involved his bodyguard needing to take steps to rectify the situation which unfortunately meant the ‘death’ of James’ earthly body.
A camouflage effect made the team think they knew James which only had a 100 mile radius which was discovered by Gwen after a trip from Cardiff to Manchester.
This meant the team had to come to terms that a valued member of the team as well as a best friend to each did not actually exist, especially affected was Gwen who had been conducting an affair with James and was about to leave Rhys.