The valley of the shadow - Carola Dunn

A cryptic message spurs Eleanor on a frantic search for a refugee's missing family.

While walking her dog with friends, Eleanor rescues a young half-drowned Asian man out the water.
Delerious and concussed, he talks about his family being trapped in a cave. While the young man, unconscious by this stage, is whisked away to a hospital, a desperate effort is mounted to find the family of which he spoke.

The local police inspector presumes they are refugees from East Africa, abandoned by the traffickers who brought them in, so while the countryside is being scoured for the family, Eleanor herself descends into a dangerous den of smugglers in a desperate search to find the man responsible while there is still time.