what I remember; Modern day guy Wales up in Forrest injured, female protagonist (daughter of a tribe leader) grabs him dragging him back to tribe outpost to be turned into food. Due to her position in tribe she didn't currently need more food so keeps MC as slave in broken down hut, given meagre rations to ensure he lives MC is allowed to heal before made to work. Winter comes tribe retreats to back of a cave with their animals for food leaving the 2 slaves of tribe out in elements in the 2 broken down sheds. MC uses modern techniques and knowledge to hunt, manages to fish in river for more food and to gain pelts to protect from cold, trades fish (for tribe it's rare) for assistance in chopping wood and fixing up shed. Other slave gets jealous tries to murder MC but fails and dies, MC drags him into Forrest where he is eaten by wolves or something. MC gains a broken sword from the other slave.
After winter he is fully healed and rebuilds his hut gaining attention of his master.
The tribe outpost travel back to tribe (main tribe) where MC builds a Hutt for tribe leader (female leads father)
This tribe is part of a group of tribes under a stronger tribes authority which is about to start a war with another group of tribes.
MC escapes from captivity and is then captured by another tribe again a slave