 McGarrett receives a call from a Skid Row bum who says he has vital evidence in a mainland case. When McGarrett and Danno arrive at the man s fleabag apartment, he s disappeared, with a trail of blood indicating he was robbed and shot but managed to escape. In his mattress, the investigators find some silver certificates which they recognize were used as ransom money in a mainland kidnapping eight years ago where the victim was murdered and the kidnappers escaped. In the interval, silver certificates were removed from circulation and are therefore now "hot money." Five-O figures out that the man who called them was the bagman for the killers and took off with the loot, and they ve finally tracked him down. When a woman spends two $20 certificates at a dry-cleaning establishment, Five-O realizes she s one of the killers, but can t find her yet. They do find the dying man, though, and he tells Five-O that a husband-and-wife duo shot him and took off with most of the certificates -- and that the duo s mainland accomplices, whom they also stiffed, are in Hawaii looking for them as well.