Thunder boomed against the lighthouse, the wind a furious beast. Flynn clutched the glowing pebble, its warmth flooding him with visions.

"Intrigued?" A voice like crackling embers materialized beside him. An old woman, her eyes dancing with starlight, leaned closer. "The Heart of the Sea. It chooses its bearer, and tonight, it chose you."

Doria vanished, leaving Flynn with the throbbing stone. He squeezed his eyes shut, the warmth morphing into an impossible sight: an underwater city shimmering with bioluminescence. A mermaid, emerald scales glinting, smiled. "Welcome, Flynn. The Heart of the Sea brought you. We need your help."

His mind reeled. "This… isn't real!" he sputtered.

The mermaid chuckled, a melody of waves and wind. "Oh, it's real enough. And you won't believe what happened next..."

She weaved a tale of encroaching darkness, a forgotten prophecy, and a perilous quest. The lighthouse keeper, heart thundering, felt the pebble pulse in his grasp. This wasn't a dream. The storm, the stone… it all led here.

"What must I do?" he asked, his voice finding its strength.

The mermaid's smile deepened. "That, brave Flynn, is for you to discover. The magic chose you, and it believes. Now, let the adventure begin."

And so, the night the storm brought magic started a journey that would echo through legends.