Image courtesy of dangdang.com
Gallen is only in part 2. Other cast members include Kenix Kwok, Gigi Lai (part 2 only), and Joe Ma.
I watched part 1 awhile ago and am currently watching part 2. These series are alot more hardcore when it comes to cop work compared to the DIF series. It's difficult to expect a happy ending to the cases all the time. Unfortunately, TVB doesn't seem to make 'em like this anymore.
Review of part 2 by sukting: http://www.spcnet.tv/reviews/review.php?rID=360