This is the Oh my god, the President is going to ask me about this and I need to be able to speak intelligently. cliff notes version.
Released in 1981, The Great Muppet Caper records the events that occur when two twins Fozzie and Kermit travel to London to interview a famous fashion designer who was the victim of several jewel thefts. The paper that they work for, the Times, doesn't quite have enough money to send Kermit and Fozzie in the actual cabin of the aircraft, so they are forced to ride as cargo. They are unceremoniously dumped out of the aircraft and their boxes parachute into a lake (much like resupplying soldiers in WWII). They choose to stay at a Wacky hotel. Kermit meets, and falls in love with, Ms. Piggy, who is acting as the designer's secretary even though she wants to be a fashon model herself. Charles Grodin, the lead jewel thief, is also smitten by her and when she refuses him he frames her in another jewel theft(the bastard!). Kermit and the gang from the Happiness Hotel are determined to catch the bad guys in the act of stealing the baseball diamond.
Much Hilarity ensues.
Thanks to Imdb for helping me get the date correct. The rest came from my vicodin fevered mind