WASHINGTON (AP) — Sometime earlier this year, one of the most elite social events in Washington took place, but without any fanfare or news coverage.

It drew about 1,800 attendees and Grammy-winning rocker Lenny Kravitz performed. Yet there were no written invitations, and the actual date and location were carefully guarded secrets.

The annual charitable event is mischievously known as Spookstock. While many Washington insiders, let alone the public, haven't heard of it, the gala has become a centerpiece for the capital region's tightknit intelligence and military special operations communitie...