The Soulless Sinners M.C. is a spinoff of the Golden Skulls M.C. 

First mentioned in Vicious Book (#10 of the Golden Skulls) the Soulless Sinners are not the typical motorcycle club. Billionaires, the brothers of the Soulless Sinners straddle the line between public perception and their true nature. 

These series of books will be a continuing saga and should be read in order. These books are dark with many triggers.