On Cold Ground is the fifth instalment in the Detective Karen Hart series, set in and around the cathedral city of Lincoln. The prologue begins with DS Hart off duty and spending time with her boyfriend, Mike Harrington, who she had been seeing for 6 months. It's bitterly cold and they're strolling through the stalls at Lincoln Christmas Market not realising a man has been following them for the past 3 hours. Referred to as "Sparrow" he watches every move they make as ordered by his boss "Eagle". He spots them walking more briskly now towards the cathedral and refers to Karen as the dangerous one out of the pair. While walking past the west front of the cathedral Karen and Mike hear a bloodcurdling scream. It seemingly came from a middle-aged woman who Karen recognises as Eunice Greene, and she tells her that there is a body in the chapel. She had been sitting at her desk in the cathedral collecting fees from those who wished to explore inside as it helped with upkeep. Karen enters the Morning Chapel, while a shaken Eunice stays outside, and finds the body between the first and second pews. It was the corpse of a man with brown hair, greying at the temples. His forehead was a bloody mess; he had been mutilated and a cross etched into his skin hinting at a possible ritualistic killing. A ligature mark snaked around his neck indicating he was strangled. They soon discover that the body is that of 46-year-old Lloyd Nelson, a member of the amateur cathedral choir who practice there every Tuesday. Trust Karen to be in the right place at the right time on a leisure day to be the first on the scene of a gruesome and bloody murder. A short time later, DI Morgan, the lead investigator on the case, finds an envelope on his doormat that had been hand-delivered seemingly through the night.
Addressing him by name and referencing the handiwork at the chapel, it suggests Lloyd had many dirty secrets, such as beating his wife and embezzling money, and that now he had been cleansed of his sins, before being signed as "The Cleanser". Due to this Morgan must be removed from the investigation and Karen and PC Sophie Jones are assigned a new team with DCI Churchill at the helm, an insufferable, arrogant man who may be one of the corrupt officers that DS Hart has been looking into in a Major Corruption Enquiry that is still ongoing. It is believed these corrupt cops conspired to run Josh, Karen's husband, off the road killing both he and her daughter Tilly. There is also a current investigation into a hit-and-run where a young cyclist, 12-year-old Sam Pickett, was travelling home and left to die alone by the roadside. Then another body is found; this time of 27-year-old Laurel Monroe discovered by her sister at a motel. Can Hart and her team find the connection between these two victims and stop this ruthless serial killer? DS Butler has penned the most gripping and addictive instalment of the series so far and the complex, multilayered plot with several different but often converging strands holds you captive throughout. From beginning to end I was riveted by the intrigue, suspense and twists and turns aplenty and the liberal misdirection meant I couldn't figure out the serial killer's identity. With regards to the killer’s case, there is little in the way of forensics or solid evidence, the corruption case is still playing out and Karen continues to struggle with the loss of her husband and daughter. Told from Karen and the unidentified killer's perspectives, this is a fast-paced and enthralling read with an exciting, explosive and action-packed conclusion. Highly recommended.