I had 4 one on one interviews over the course of two interview rounds. My first round was with two managers and the second one with one manager and one principal. All interviews consisted of CV-based questions and regular interview questions, such as "Tell me about a time...". The second part of each interview consisted of case studies. They were a bit of hit and miss with me as I did quite well in the first round, but not in the second round. I received good feedback after the interviews. I would suggest going through both Vault.com and Case in Point guides for case studies. In addition, you need to practice with someone. I believe that was my one problem as I had a difficult time going through some of the more complex business issues out loud and developing my thoughts to the consultants. Good luck.