The Dagda is a "good god" in Irish mythology. He had great magic powers and a beautiful harp that could control weather and crops. More importantly, this magic harp could control people's emotions and feelings.
By plucking the strings of his magic harp, the Dagda could instantly get all his warriors ready for battle. When they returned home, the Dagda played his harp again. This time the magic music caused the men to be calm and forget about any battle wounds.
Once upon a time, during a war, the enemy tribe stole Dagda’s harp and took it to an old castle far away. Dagda followed the tribe to the castle and called out to the harp, "Come to me, my beautiful harp."
The harp sprang from its place in the middle of the castle banquet hall and dropped in front of the Dagda. He played 3 loud chords that he called the Music of Tears and everyone in the castle began to cry.
Just as the warriors were about to draw their swords, Dagda plucked the harp strings and played the Music of Mirth. All the warriors began to laugh hysterically.
The Dagda struck the harp again. This time the notes were soft and sweet, pure and soothing. This was the Music of Sleep. Everyone but the Dagda dropped to the ground, closed their eyes and nodded off to sleep.
When the Dagda was certain that everyone was fast asleep and unable to move, he took the harp, left the castle, and returned to his land with his magic harp unharmed.