I found Oliver to be the most intriguing character in the story. It’s obvious he’s hiding something, which we don’t learn about until late in the book. Also, he has so many opportunities to do the right thing and he fails time and time again.
Oliver is an intriguing character – he had a warped sense of familial loyalty to people who were generally pretty terrible (especially Kip – who he claimed was like a father to him, but he clearly realized was a greedy liar who only really cared about himself). He thought he loved Tammy, yet really expected her to just let her father’s killer walk away with no consequences (and himself as an accomplice).