This 2K teaser sure looks a lot like BioShock
BioShock publisher 2K has posted a teaser image which fairly reeks of the seminal shooter series.
BioShock isn't mentioned by name in the teasing tweet below, but Poseidon Plaza is a location in Rapture, and eve is the substance harvested from Little Sisters to power plasmids.
There are all sorts of theories as to what the tease might mean but so far nothing concrete has surfaced. We'd like to think a new game or DLC pack is in the works, but it's a bit confusing that the tweet came from 2K UK, not 2K's main account. That might mean some sort of local promotion is on the cards.
2K hasn't said anything else since the teaser was published so I guess we just sit tight and wait. Original BioShock developer Irrational Games has been disbanded, with creator Ken Levine moving onto smaller projects, but 2K owns the property and is not averse to having other teams work on it, as with BioShock 2.
Levine said recently that the long awaited BioShock Vita game seems to have been shelved, so it's probably not that.