A time-traveling, end-of-the-world police procedural, Extremity is True Detective if written by Philip K. Dick.

When once-renowned police detective Julia Torgrimsen is brought out of forced retirement to investigate the murder of Bruno Donaldson, a billionaire she worked with whilst undercover, she doesn't expect to find two bodies. Both are Bruno--identical down to the fingerprints--and both have been shot.

As the investigation sucks her back into the macabre world of London's rich elite, she finds herself on the hunt for a mysterious assassin who has been taking out the wealthy one by one. But when she finally catches up with her quarry, she unveils an entire world of secrets: impossible documents about future stock market crashes, photographs of dead clones, and a clandestine time-travelling conspiracy so insidious it might just mean the extinction of the entire human race.

If Julia is to have any chance of preventing this terrible future, she'll have to revisit her own past, the terrible choices she made undercover, and the brutal act that destroyed her once legendary career.