A con man arrives and his gaming device changes the odds on the Promenade.
Odo jails Martus Mazur, an El-Aurian con man, and in the cell he gets a strange gambling device from a dying old man. His luck turns at once: the charges are dropped, and he opens a bar and gaming hall that steals Quark's customers.
Bashir and O'Brien have a racquetball rivalry, which Quark turns into a public match to win back business, and O'Brien plays far better than he should. The crew realises that Martus's machines are distorting the laws of chance across the station. Martus's luck runs out, and Sisko and Dax destroy the device.