Tabitha has a new flying saucer and she and Darrin have great fun playing with it. When Aunt Clara babysits while Darrin and Samantha are out, the saucer accidently flies out the window so Aunt Clara tries to retrieve it by magic, but instead a REAL alien ship from another planet lands in the Stephens' back yard and it even has a couple of aliens inside!
Naturally, Mrs. Kravitz sees it and immediately calls in the Air Force to invrestigate but Darrin, thinking clearly tells the investigators that he is in the ad game and that he built the remarkably realistic ship to use in an ad campaign. The senior officer is satisfied but Mrs. Kravitz and the junior officer definitely are not!
When the aliens, Orvis and Alpha, are enticed out of the ship for breakfast, they are seen by Mrs. Kravitz and they must zap her with their "N - Gun" - which stands for 'niceness gun' so that she is pleasant to them and believes them to be actors working for Darrin's ad campaign.
All is right with the world when Aunt Clara sends the aliens back to their home planet, but it was a near thing, especially with Mrs. Kravitz poking around!