Gotham Underground is a 9 issue mini-series involving a big time turf war between just about every criminal in Gotham City both meta-human as well as common mobsters. Aside from that, several random criminals are turning up missing. Not due to gang related violence but because the Suicide Squad has been abducting them. Of course as you all know by now we all know those criminals are being sent on via boom tube to their new home somewhere on a planet far far away. It's also worth mentioning that even criminals in jail are getting abducted. In some cases the Squad is working with the Penguin to lure fellow criminals for "business meetings" in order for the Squad to ambush them.
But not all the abductions are going as planned for a number of reasons. Like the case of some punk called Great White Shark. You see here The Squad busting a hole through his jail cell to get to him. But upon finding him he starts doing some major trash talking to Bane about how he's not that tough anymore like when he broke Batman's back and how his venom must have given him brain damage. So Bane looses his cool, beats the shit out of him and throws him out of the opening in the cell wall several stories down presumably to his death. Now take note that The Squad here still has Bane and Deadshot on it. Which means that Gotham Underground must have taken place between the Raise the Flag mini-series and Salvation Run #2. I imagine it was shit like this that eventually led to the decision to having Bane exiled to the prison planet. I didn't have much like finding clip art for this series unfortunately. Aside from the clip art above all I could find was some uncolored pages from comicart.com. But at least looking at the black and white panels will give you some idea of what was going on.
Also, the Gotham Underground mini-series has it's own Wiki page so if you want to read up about it in more detail it's there for you. It's a fairly brief read and it will help you follow what's going on in these panels: http://en.wikipedia.org/wiki/Gotham_Underground