If you haven't had the pleasure of reading a Stephanie Plum mystery, this is not the place to start. While all the players that have earned Evanovich's series a legion of fans dutifully hit their marks -- from wisecracking, bumbling Trenton bond enforcement agent Plum to opinionated Grandma Mazur to hunka-hunka Italian cop Joe Morelli -- the novel seems a little rote. The 10th Plum mystery in as many years, ''Ten Big Ones'' clearly suffers from book-a-year syndrome. This time, Plum inadvertently witnesses a convenience-store robbery perpetrated by a murderous gang member wearing a devil mask and becomes a target when she helps track him down. The cantankerous nature of America's nuttiest bounty hunter still beguiles, but the plot is thin and what's supposed to pass for funny, doesn't.