This is a Ghost/Batgirl team up. The Batgirl in question is Cassandra Cain. And Ghost is a woman, Cameron, who can-- well-- become a ghost, something about her mass or whatever. She can get through people, things. She's based in Arcadia, and the case that brings her into contact with Batgirl and Oracle is a missing girl that no one else cares too much about finding.

In Gotham City Batgirl and Oracle are trying to find a young woman who goes missing after Two Face blows up the Diamond Exchange.

There's also a Doctor Greymatter as well as the 'Engine' from the title.

I didn't totally love the team up, but I liked the art, and the story wasn't too bad either. I probably would have liked it more if I had read any stories with Ghost in them before. ( )