“Bert, the last time we switched, somebody died,” Nan Tatum tells the twin who asks her to fill in as Stephanie Whitman’s Girl Friday for just one Saturday. But Bert is so desperate to go to a job interview that might rescue her from her harpy of a boss that she insists. So Nan agrees to cover for her sister, arriving at work just in time to get knocked down, in the story’s best-judged anticlimax, by a well-dressed fugitive who’s merely broken into the office and burgled it. It’s not until Monday night that Stephanie’s murdered, and by that time, McCafferty and Herald have already gotten all the mileage they’re ever going to get out of Bert’s awkwardness in having to describe and identify a perp she never saw. Instead, the sisters blunder into a scam involving the late Stephanie’s uniquely hardball approach to her divorce practice—a scam most likely to beguile readers who don’t know very much about the rules of evidence concerning tape-recordings brought to court. In between the twins’ gamely implausible visits to Stephanie’s clients and their outraged exes, chaste Bert agonizes about whether it’s time, or whether it’ll ever be time, for her to consummate her romance with Louisville Homicide Det. Hank Goetzmann, who had a lot less trouble persuading Nan before he took up with her sister. The twins’ third (Double Exposure, 1997, etc.) offers more gently reliable good humor virtually undisturbed by the rudimentary mystery.