When one person from your past returns bent on revenge it usually spells trouble, when several come together to collaborate as a single unit, it is time to get very worried.
As part of a complex revenge plot, certain figures from the Commander's past has set him a series of challenges, the reward for completing them successfully is he gets to save Tracy's life.
Into this emerges another figure from the past but is he all he seems and can he be truly trusted?
Concluding the 'District Line quadrology, this episode in the series sees quite a few forgotten characters from the past re-emerge.
Also for the first time we get a glimpse into the Commander's past and the first hints of the circumstances surrounding the 1969 'Lewisham Diamond Heist' and its consequences which forms the core of the next novel '...