You never know who might take the podium at a Donald E. Westlake appearance. This is a man who once hosted a roundtable discussion by four authors, each a pseudonym of his (and he has at least five more). It could be Westlake himself, Academy Award nominee for The Grifters screenplay and author of numerous comic capers. His most recent is far more disturbing: The Ax follows an unemployed middle-management family man as he oh-so-reasonably sets out to kill his competition for a dream job he will later make sure is vacant. Or perhaps Richard Stark will appear. Backflash is the latest thrilling addition to his series about the professional thief Parker. The first, The Hunter, became the lame new movie Payback, but it was also the source of the vastly superior Point Blank. Westlake was once asked how he decided whom he wrote as on any given day. He replied that when it rained he was Stark, when it was sunny he was Westlake. So check the weather report before heading downtown. One or more of these writers will be interviewed by Pulitzer Prize-winning Washington Post Book World Senior Editor Michael Dirda at 6 p.m. Tuesday, Feb. 16, at the National Museum of American History’s Carmichael Auditorium, 14th & Constitution Ave. NW. $13. (202) 357-3030. (Mark W. Sullivan)