How to get the conversation back on track?

Suppose you need to discuss an important issue with someone. But you feel that the interlocutor is trying to "weasel out" from the topic you had in mind. How does one delicately get the conversation back on track? Lean back in your chair and take a break. As soon as you feel their undivided attention, tell him that you met directly to discuss another issue. Name it and tactfully but persistently ask the interlocutor to return to the discussion of the intended subject.