I have one major problem, and it's that this would have been much better as a two-parter.
Quinn's double's experimentation with sliding ended in disaster when his extremely powerful wormhole sent the entire human population to another Earth. The very arrogant double proves to be very annoying to the team, especially our Quinn. Together, they decide to slide to the other world to find out what happened to the five billion people. They discover when they slide that the arrival of five billion extra people caused havoc on that world (now with a population of 10 billion and two sets of each person) and that a man called The Boss is calling the shots. The team decide to send everyone back to their original world, but need the power to do it, so must travel to the Boss's power plant to get to it.
This Slidewave device is very cool. It's a huge wave that transports an entire population to a new Earth and avoids the need for the wormhole. We also get to see Quinn's house for the first time since "The Exodus," but it's a new exterior and doesn't even seem to be in the suburbs. The interior however seems similar in several ways (especially the staircase) to the house in the "Pilot."
We also finally seen Quinn's basement again, though it's been destroyed completely by Quinn's double. Also, the major effect of the week, the Slidewave, was very cool. The two Quinns standing together were seamless, worthy of movie effects they were so well done. The supporting cast this week very good, but the nun and her double were the best, particularly since the doubles were complete opposites. Quinn's double comes up with the best line this week in response to the gun toting nun – "Are you on crack, sister?"
I'm waiting for a Remmy story, hopefully to deal with his growing problems.