NEW VIDEO EXCLUSIVE: 'Pirates of the Caribbean: On Stranger Tides' Hears the Siren Song

Ahoy, matey! Mark Steines exclusively unearths some serious treasure from the Los Angeles set of the hugely anticipated 'Pirates of the Caribbean: On Stranger Tides'! Watch the video!

Johnny Depp is back as the loopy Captain Jack Sparrow for this fourth 'Pirates' outing of the billion-dollar franchise from uber-producer Jerry Bruckheimer, and this time he's joined by Penelope Cruz as Angelica, a seductive woman from Jack's past.

"Well, [Penelope] is looking for the Fountain of Youth, just like Johnny, so it's a race to the Fountain of Youth," says Jerry of the plot. "There might be a little romance, but I can't tell you too much more."

Jerry adds, "We've got beautiful mermaids, they're absolutely beautiful, but they're killer mermaids. They're very dangerous. They're like the sirens in Greek mythology."

'Pirates of the Caribbean: On Stranger Tides,' directed by Rob Marshall ('Nine,' 'Chicago'), sails into theaters May 20, 2011 in 3D, and Jerry assures us that it will look amazing.

"We're doing it I think the right way," he says. "We're [shooting] it in 3D, not converting afterwards, so we have 3D cameras that are filming the entire movie. So you're seeing the real thing."

And any hint as to whether or not there will be a fifth or even sixth installment?

"If people show up for four, we'll certainly try to do a five," says Jerry. "We're already working on a story and we've laid out some really interesting beats of kind of things we'd like to see in five. So that's where our writers are working right now."

Watch ET for more 'Pirates of the Caribbean: On Stranger Tides' exclusives!