Andy Blake is no sooner married to Arab that he realizes his home is not a love nest but an arsenal. True, the fragile, blonde Arabella had won prizes only in shotgun contests, but she didn't discriminate against rifles and pistols. As Andy wistfully says, ''The worst thing about Arab's guns is that they come in handy. She can track down trouble the way a detector spots land mines.'' Andy and Arab are plunged into this bang-up mystery when they attend an auction sale where a pistol starts a bidding contest between two oddly assorted customers. Andy, who also knows his guns, is sure that the pistol isn't worth more than thirty bucks. He is therefore both flabbergasted and interested to hear the bidding skyrocket to two hundred dollars, especially since one of the bidders is a red-head whose legs he finds the most interesting exhibit at the auction. As Andy and Arab leave the auction he idly says to her, ''The person who bought that rod make a down payment on a time bomb. That red-head wasn't bidding in the hundreds just to stimulate interest in the auction in general. I got a hunch the new owner will meet a lot of unpleasant people. Who bought the thing?'' Taking his arm, Arab answered happily, ''I did.''