All-Night Party (Fear Street Book 43)

Fear Street -- Where Your Worst Nightmares Live...
It's Cindy's birthday, and her friends are throwing her a surprise party on Fire Island. It's a private party -- no parents, no cops...in fact, no one around for miles.
Except there's a madman loose on the island. A murderer who quietly crashes the party.
And he wants to dance with the birthday girl...