Joanna Lee wrote this far out episode, behind many sitcoms in the 60s, though her claim to fame was playing one of the aliens in Ed Wood's cult classic, PLAN 9 FROM OUTER SPACE. That story alone is sitcom material.
Gilligan has a twin, but not an ordinary twin -- a Russian SPY. One thing, it may have all been inspired by MISSION IMPOSSIBLE. Russians seemed to make the best bad guys and, in this case, always stepped onto the island to start some sort of trouble. If you're a sitcom fan, it was the same story with GET SMART.
This all gets the real Gilligan in a mess; he now has a goofy twin strutting around the island. The agent underwent plastic surgery to spy on the castwaways. BIG question: WHY them?
The highlight, as noted by other reviewers, is a classic MARX BROTHERS mirror routine between Gilligan and his double. The only debit is its too short.
Notes indicate Bob Denver, during filming, had a bad case of the flu. You can notice that in some early scenes as he looks a bit tired and worn. In the final scene, Gilligan is resting in his hammock, and I think it was done that way to get him off his feet.
Well directed by Jerry Hopper, who was a WWII hero, awarded the Purple Heart. He did a ton of tv shows, also dramas, like PERRY MASON and the FUGITIVE.
Best prop slash invention is the spoon and fork combo transmitter the professor discovers, that belonged to the Russian spy.
SEASON 3, EPISODE 2 remastered CBS color dvd box set. Released 2005 and 2012. The cover is the absolute best.