I just had an epiphany of sorts and have formed a wild ass theory about Angel, Scratch, and the rat. Bear with me on this.
In 20-3 after Scratch said she had to drop Pippin off, Tardust asked "What about the other one?" Scratch replied "We still have them." Tardust then said he meant the other one, insinuating he was talking about the rat. Scratch replied that they hadn't heard anything in awhile.
So it sounds like the Mallers have some unknown person in their possession who will probably turn out to be important. So here's where my theory comes in.
We've been wondering how Angel and Scratch know each other and some have wondered if Angel has some kind of criminal past. But what if he isn't the one with the criminal past? What if he knows someone with a record. Someone who may have been locked up in Eastern Bay? He could have met Scratch while visiting this person (with Scratch there to visit Latch at the same time). Scratch then recognizes Angel later, finds Angel's person (who would have been with the Mallers after they got out of the prison), and uses that person as leverage to force Angel to rat on the Tower.