Walker and Munoz return to the scene of their first investigation. But this time it’s a cold case, and many of today’s modern investigative tools won’t help them solve it.

As they make some painstakingly slow progress, additional challenges stymie their efforts. And then a new present-day crime, precipitated by the revelations surrounding the cold case, force them to shift their focus entirely.

When the investigation begins to stall again, they get new information and evidence from two unlikely sources. But can they use it … or trust it … and will it be enough.