On the Rocks — Kerry J. Donovan

A schoolboy lies alone and dying on a Scottish mountainside.
A highly experienced rescue team can't find him.
One man is the boy's only hope.

When news of Martin Princeton's disappearance reaches international fugitive and former Royal Marine, Ryan Kaine, he abandons the evidence that could help clear his name and heads to the Scottish Highlands. Officially, the authorities want Kaine in custody. Unofficially, there's a bounty on his head.

Still hampered by injuries from the events that turned him into the most wanted man in Europe, Kaine uses the heavy burden of killing eighty-three people aboard civilian aircraft Flight BE1555 to fuel his new mission. He will protect the grieving families, The 83, at all costs.

Armed only with charm and an intimate knowledge of the region, Kaine must convince the rescue team of his good intentions and find out everything he can about Martin's disappearance before they discover who Kaine really is.

Using his mountaineering knowledge, his special forces training, and his rapport with the locals to help him find the missing boy in time, Ryan Kaine is …

On the Rocks.

Can be read as a standalone novel.

If you like Lee Child's Jack Reacher, Mark Dawson's John Milton, and Robert Ludlum's Jason Bourne, you're going to find the Ryan Kaine's 83 series compulsively addictive.