The first of BioShock Infinite's three promised instalments of downloadable content is finished and goes on sale today, Irrational Games has revealed.

However, the bigger news is that the second and third DLC packs will form a two-part detective story set in Rapture.

"I know, right?!"

Called Burial at Sea, it will star Booker and Elizabeth as private investigator and femme fatale respectively, and you will get to play as both of them.

The DLC pack released today is called Clash in the Clouds. It's a wave-based arena game that makes the most of Infinite's varied combat system.

It also includes new voxophones, written by creative director Ken Levine, as well as kinetoscopes and other unlockable goodies to keep fans happy.

Clash in the Clouds will cost $5 on Steam, where it should be live at 12pm ET / 5pm BST / 6pm CEST.

Irrational said PlayStation Network and Xbox Live versions will appear as soon as Sony and Microsoft push the button on their weekly updates.

So is Clash of the Clouds any good? You can find out by reading my BioShock Infinite: Clash in the Clouds review. (Spoiler: it's not bad, as stopgaps go.)

As for Burial at Sea Episode One and Two, we don't know exactly when they will be released, but Levine indicated to me that Part One would arrive this year, while Part Two will probably be along a little later.

Burial at Sea is set on New Year's Eve, 1958, the night of the bombing that was the beginning of the end for Rapture. In the first episode you play as Booker, and then in the second episode you play as Elizabeth.

"At the very beginning, you're Booker, private detective in Rapture, in your office and this woman comes in, and you two don't seem to know each other, and we don't explain that," Levine told me.

"We always like to put people in a place where there's a story that ends up making sense, but we don't want the obvious... We like people immediately having a sense of wondering what's going on."

Interestingly, both Clash in the Clouds and Burial at Sea are entirely new content, with Irrational keen to avoid scraping things back up off the cutting room floor.

"We have a bit of a different approach to some people to DLC," Levine explained to journalists who assembled at a Boston hotel for the unveilings.

"When we started this, we really tried to listen to the fans, and to us the fans were clearly saying to us, look, we want the A team on the DLC, we want the same team who did the actual game, we don't want it to be stuff that's on the disc, we don't want it to be stuff that some marketing guy came in and said 'leave that aside'.

"So basically the day we finished - literally, pretty much the day we finished Infinite, we went to work on the DLC, starting pretty much from scratch on the game content."

While Clash in the Clouds is "a sort of a compromise between timeliness and scale", with no huge build-up, Burial at Sea is "a bit of a love letter to the fans", Levine said.

"We're pretty deep into this one - we're about to enter beta. I've been working on this with a lot of the narrative team since we shipped Infinite.

"So it's a two-part experience... The second part has a slight twist to it. You play Booker obviously in the first one, but we were listening to the fans and we know how they feel about Elizabeth, and we decided we wanted to shift things around a little for the third one, so the player character in the third DLC, you get to play Elizabeth, and the gameplay is quite different as her.

"She's not the tank that Booker is, and we'll see how all the story's coming together."

To read more about that, check out my BioShock Infinite: Burial at Sea interview with Ken Levine.