The story is, in many ways, fairly typical of Heinlein's work in this vein: He was working hard to present Life Off Earth in a positive light, in hopes of luring humanity into investing in the Space Program, which was one of his major interests.
A physical chemist and his wife (the MacRaes), who have been in residence in Luna City on the Moon for some time, spend much of their time volubly regretting having ever left Earth. When this attitude results in social conflict with "Loonies" who love their home, the pair feel isolated, misunderstood, and put-upon. They decide to return "dirt-side", only to discover that the Earth of their imaginations bears only the faintest of resemblances to the actuality, which includes things unheard of in Luna, like smog, unpleasant weather, the common cold, and repairmen who refuse to make house calls. Ultimately, they discover that all they really want is to go back to Luna City, where they are welcomed with open arms by their peers (now that they have stopped complaining all the time) and settle down to be happy "Lunatics".