Formerly, the "prisoners" problem was used by the author in his teaching chiefly as a process activity, with the intention of promoting certain investigative techniques: the idea of starting with a smaller problem (say, 10 prisoners, guards and cells, rather 100), and the importance of finding an effective method for displaying what was going on. At some point in the proceedings, he would have some of the students act out the 10-prisoner problem, which makes for a fun lesson, and ultimately all the groups he tried this with would discover that the square numbers were the solution. More recently, however, he has been using this problem as an opportunity to deal with the terms factor, multiple, prime and square and to assess learners' prior knowledge of these concepts. In this article, the author describes how he adopted a new perspective on a familiar investigative task. Where he had originally seen the "prisoners" problem as a nice way to introduce certain investigative skills, he now realises that it can be the basis for a lesson which focuses on both skills and knowledge; both process and content.