Right. So the Rift that Torchwood Three was built upon, you humans figured out a way to harness the energy between worlds to utilize it as an unlimited source of essentially free energy. This free energy came at a cost, as it usually does. Within a year and a half, it was detected that death rate in the other world sharply increased, seemingly without reason - Earth Prime was siphoning off all Dimension B's life, and despite reports of the devastation it was causing, the government did nothing to stop. Greedy for more, they managed to locate three other dimensions that they could potentially tap.
Colonization all over again. Rule Britannia.
Blah blah blah, I show up, and with Toshiko, Lisa, and your help, we expose the so-called 'Free Energy Project' for what it was - genocide on a global scale. We shut it down, closed the Rift. There's a huge energy crisis in the UK, a governmental failure. It's not fun.