Long ago in the time of the Fianna a huge monster lived in Lough Derg. He had caused great havoc in in the neighbourhood and no one could approach the lake except when he was asleep. He had also eaten about thirty people.
When Fionn heard this he made up his mind to kill the monster. He then got the Fianna ready and set out in the direction of Lough Derg. When they arrived the monster began to splash the water until they were all drenched.
They then waited until he was asleep