Tartarus is book 2 in the West of Hell series.
With Gehenna burning behind them, Karen and McCall had hoped to escape by using the railroad. When one of the moaners is pulled aboard by concerned passengers, the unlikely duo have to survive a train ride from Hell.
As they head further West, toward the mighty Tartarus River, the outlaw and the prostitute must deal with not only an ever increasing army of the dead, but also with the machinations of the living.