The last time this much mystery surrounded a plate of French fries, Nancy Drew was trying to solve the Case of the Freshman Fifteen. This year, for about the price of a paperback ($10), local sleuths can try their hand at figuring out how the fries at the Federal are so darn good. Lean on the server, and he might admit they are hand-cut and soaked in a preparation before being lightly fried. Sweet-talk the bartender and she might spill that the fries are left to sit for a while before being refried for the customer. But isn't it a little suspicious that chef Cesar Zapata knew to prepare them before they were even ordered? And what about the proprietary blend of herbs and spices, nuanced enough to make Lowry's seem like lye? How to account for the fried Lake Meadow egg laid across the top, just runny enough to glaze the spuds when a knife plunges into the heart of the yolk? Or the chilled ketchup that calms the edges of the seasoning while also making for a strange temperature speedball? Sure, Zapata will fess up that the ketchup is a twist on a generations-old family recipe, but isn't it a little suspicious that his great-grandfather knew the recipe and is now dead? The menu says "Townpark Fries," but maybe it should read "murder."