'BioShock Infinite' Rapture trailer goes retro

Period piece "BioShock Infinite" is getting ready to launch a two-part dispatch of extra story content that delves into its predecessor's milieu.

Period piece 'BioShock Infinite' is getting ready to launch a two-part dispatch of extra story content that delves into its predecessor's milieu.

'BioShock' and direct sequel 'BioShock 2' took place in the underwater city of Rapture, circa 1960.

And while 'BioShock Infinite' eschewed sea for sky, the 60s for the 1890s, an alternate universe motif allows upcoming expansion 'Burial at Sea' to revisit the submerged city of its forebears.

This appetite-whetting video takes on the style of an archive investigative reportage, tracking a mysterious suitcase that washed up in the northeast USA, helping to reintroduce the Rapture concept.

The trailer also arrives as the PC version of 'BioShock 2' extracts itself from Microsoft's retiring Games For Windows Live system and transfers over to the Steam Network's copy protection system.

Those who own 'BioShock 2' on Steam have found themselves receiving complimentary copies of well-received expansion 'Minerva's Den,' whose lead designer went on to co-create this year's much feted 'Gone Home,' set in an abandoned 1990s Oregon residence.

'Burial at Sea' will be the first story-based expansion for 'BioShock Infinite'; a release date is yet to be announced for the $15 download.