It was a mistake. Percy had the feeling the second the four of you stepped off the train. Annabeth had insisted that you go and see the Gateway Arch, so you did.

You got to the top, and that's when the trouble started. Echidna had shown herself, her Chimera growling.

You rush Annabeth and Grover down the emergency exit stairs, getting ready to help Percy. He hands you Riptide. "Take this."

But when you did, he pushed you back and slammed the door closed, turning to face the Chimera.