Zim goes on an outing to the downtown area in order to test a new guidance chip he installed in GIR, but when GIR removes the chip before leaving in order to store a cupcake, Zim and GIR are left lost and have to resort to public transport to find their way back. Their journey home is complicated further by Zim temporarily losing his vision by looking at the sun, his disguise being mistaken for that of a bank robber, and his escape from the police being wrecked by GIR replacing his extra rocket fuel with tuna fish.
