In Sharky Dexter's casino in Los Angeles, a man beats the crooked roulette wheel. He places a large bet on number thirteen, which comes up. He lets it ride for a second time and wins again, then stakes the lot on thirteen again -- ald calmly walks out with a million dollars of winnings! When Sharky hires Johnny Merak to find the man who's taken his money, there's a spate of murders -- with Johnny himself a candidate for death ...