The ‘Missing Link’ DLC for Deus Ex: Human Revolution will be released on 18 October, Eidos Montreal has confirmed.
This add-on will fill in the blanks on Adam Jensen’s sea-voyage between Hengsha and Singapore, in an estimated five hours or so of extra Deus Ex-ey fun. If by ‘fun’ you mean ‘torture by Belltower’.
Square Enix has set the price at $15 USD, whether on PC, Xbox 360 (1200 MS Points) or PS3.
For more details on the DLC, you can watch this developer walkthrough video. But do beware of minor spoilers (in the sense that it shows you early parts of the release).