The mystery man grabbing the villains comes to the forefront in this three-part story by Dixon, Nolan and Hanna, beginning in Detective 697 (June 1996).
Two-Face is busted out during a prison transfer. Batman, Robin and Nightwing all gather when Gordon turns on the Bat-Signal (for the first time since regaining his position). They worry what he might be up to, but their concerns are misplaced. Harvey Dent is in the hands of Lock-Up, a dominatrix-garbed warden of his own personal prison. He was the one who grabbed Veezey while Batman was dealing with Poison Ivy, and also grabbed Killer Moth, in the pages of Robin.
When nothing happens with Harvey, the heroes compare notes on other villains that have gone missing. But the police are more concerned with the spreading influence of Black Mask, and one of his men turns informer.
Batman, Robin and Nightwing join the police assault on one of Black Mask’s hideouts. The leader himself is not around, but there are plenty masked gang members to deal with.
As it turns out, Lock-Up also had Black Mask on his list, and it turns out to be his misfortune to come across the police. Montoya takes the big guy down!
I really like the unusual way the issue ended. Lock-Up is in police custody, his identity as Lyle Bolton, a wanna-be cop refused because he was considered too violent and disturbed (for Gotham!) The tables are neatly turned when he points out that no one else knows the location of his secret prison, and those incarcerated will starve to death unless he is freed.
The story continues next issue.