Batman: Detective Comics by Peter J. Tomasi Omnibus

" Who's hunting those closest to Batman? Commissioner Gordon calls in the Dark Knight Detective when there's a murder at the Gotham City Aquarium, staged to look exactly like Thomas and Martha Wayne's crime scene--right down to the playbill and pearls. How does this bizarre homicide tie into the shadowy monster that attacks Dr. Leslie Thompkins? This creature looks to wage a war on Batman--and it's using Joker gas to do it"--