Hayden Panettiere by Mark Sullivan/WireImage.com Hayden Panettiere by Mark Sullivan/WireImage.com

Last night, the cast and crew of Heroes celebrated the end of their first season with an exclusive, 700-person bash at the Cabana Club in Hollywood, and TV Guide was on hand for all the excitement - including Heroes-themed drinks, a musical performance by the Band from TV, and a surprise graduation ceremony for Hayden Panettiere (Claire Bennet), who slipped into a cap and gown to be presented with her high-school diploma by series creator Tim Kring as the band played "Pomp and Circumstance."

But even though the Hero-tinis and Save the World cosmopolitans were free-flowing, the cast all proved they've all got another superpower: the ability to keep secrets. One by one, Milo Ventimiglia (Peter Petrelli), Masi Oka (Hiro), Adrian Pasdar (Nathan Petrelli), and the rest of the series' stars all carefully deflected any questions about the season finale. "Everybody dies," joked Zachary Quinto (Sylar). "Actually, I've been telling it to everyone," joked Jimmy Jean-Louis, who plays the Haitian with amazing mental powers. "The coolest thing is that I erased their memories straight after."

Greg Grunberg (Matt Parkman) did let it slip that the season finale will be "a monster episode." "It took us 20 days to shoot it. There are huge things that no one's going to see coming. We all come together, so it's going to be very satisfying for everyone."

The night was a family affair - Sendhil Ramamurthy (Mohinder Suresh) came with his wife, Olga Sosnovska, after finally managing to put their baby to bed; Jack Coleman (who plays Claire's secretive father, HRG) brought his wife, Beth Toussaint; and Ashley Crow (Claire Bennet's mom) got cozy with her husband, Matthew John Armstrong (Nuclear Ted Sprague). "These are the brothers and sisters that I never had," said a sentimental Masi Oka about his fellow cast mates.

Greg Grunberg had another job to do that night: Playing the drums as a proud member of the Band from TV. Also on stage were House's Hugh Laurie (on keyboard), The Bachelor's Bob Guiney (on vocals), Kitchen Confidential's Bonnie Somerville (also on vocals) and Desperate Housewives' James Denton (on guitar) performing "Pink Cadillac," "Mustang Sally" and "Take Another Piece of My Heart." A few of the other Heroes joined in, too: Noah Gray-Cabey (Micah) played the keyboard while Tim Kring accompanied him on the guitar. And then Hayden Panettiere grabbed the mike, singing "Hit Me with Your Best Shot" and "Ironic" - the first time she'd ever performed live.

At the end of the night, Tim Kring thanked the cast, crew and everybody's families in an emotional speech. "If you're doing this for the money," he told the cast, "we aren't paying you enough." - Reporting by Carita Rizzo

Click here to browse our hot gallery of photos from the big event!