When the current captain of Boston’s cold case unit comes knocking on Ronan O’Mara’s door he brings with him an unsolved homicide file and Ronan's old police badge. Ronan is intrigued to say the least. The case is the twenty-year-old murder of a high school math teacher. It’s the one investigation Ronan’s partner Kevin Fitzgibbon could never solve during his time on the police force. Psychic Tennyson Grimm, is happy to have his husband’s days of wearing a badge behind him, but now Ronan wants back in, begging to solve one last case. While Ronan reminisces about their good old days working cold cases for the Boston Police Department, all Tennyson can remember are the times he and Ronan were shot, stabbed, and kidnapped. Never able to deny his husband anything, Ten relents and agrees to join the hunt for the killer, who’s had two decades to cover their tracks. As new leads and old secrets come to light, the finger of suspicion points in only one direction, but when Ronan and Fitzgibbon show up to make an arrest, their suspect has vanished. When the killer steps out of the shadows to take another victim will Fitzgibbon get there in time to stop another murder? Or will this case leave Tennyson and Ronan dead cold?