According to the press release:
[T]he entire Muppets gang on a global tour, selling out grand theaters in some of Europe's most exciting destinations, including Berlin, Madrid and London. But mayhem follows the Muppets overseas, as they find themselves unwittingly entangled in an international crime caper headed by Constantine—the World's Number One Criminal and a dead ringer for Kermit—and his dastardly sidekick Dominic, aka Number Two, portrayed by Ricky Gervais. The film stars […] actress and writer Tina Fey as Nadya, a feisty prison guard, and Ty Burrell as Interpol agent Jean Pierre Napoleon.
It looks like the Muppets are paying homage to their roots. After all, the plot of The Great Muppet Caper revolved around a London jewelry heist. Director James Bobin backs that theory up, promising it's, "…a tip of the hat to the old-school crime capers of the '60s."