It's generally the easiest part of the interview process, generally the partner will not be pleased at all if someone completely unsuitable has made it through to the end.
Speak passionately to him/her and as a big part of consulting is asking questions, make sure you have some good questions, just make sure you have answers to the questions you have just asked.
So if you ask "What do you see the main challenges being in your business being over the next 12 months?" Be prepared for him/her to turn it back onto you or change the question to:
"What do you see being the main challenges in my clients' business over the next 12 months" etc.
Basically, it's a chance for him/her to test your fit against the organisation and for you to the same.