51: Damages is the fifth and final book in the 51 series. 

51: Damages​

As Sheriff Lindsay Gold and Agent Wren Gold begin to find the answers to the rest of their questions, they are also left to take stock of all the damage done to the county and themselves. The discovery of the compound leads them to the person responsible for much of the chaos and damage within the county. To get the information they need; it leads Lindsay and Wren to do things they never thought they were capable of doing. 

When things come to a head, an unlikely hero comes to the aid of others as things take a deadly turn, and not everyone will make it out alive. In the end, the biggest question is who will be left standing. For those who are left, their lives will never be the same.