The train cars had fallen over, and their roofs had shattered. Tourists were stumbling around in shock. Percy didn’t see anybody seriously injured, but the gryphons were swooping toward anything that moved. The only thing keeping them away from the mortals was a glowing gray warrior in camouflage—Frank’s pet spartus. Percy glanced over and noticed Frank’s spear was gone. “Used your last charge?”
“Yeah.” Frank shot another gryphon out of the sky. “I had to help the mortals. The spear just dissolved.”

The Son of Neptune, Chapter XXXIX