Many years ago, a group of sorcerers decided to develop a complex magical well of power that would allow them to store sorcery gifts, summon monsters to fight for them and even store some extra lifeforce. It was a project that took many years to complete and it was an extraordinary feat of arcane engineering.
There had been some drawbacks, some of which were features. Only males of their specific bloodline were allowed access to its capabilities and without enough of them around to keep it stable the thing would have... side effects. The monsters would show up by themselves, uncontrolled and feral. And if someone else tried to kill them then the surrounding nature would be drained, potentially killing the town's population if it got bad enough.
This was deemed acceptable and for a time it wasn't a problem.
Then not-as-many years ago. A family reunion ends in tragedy and the drawbacks became a very urgent problem.