All too often, valuable knowledge is lost from organisations when experts leave — both the experts and their expertise represent valuable assets (Huber, 1999). When older experts leave the workforce, they take with them significant experience and critical knowledge essential to the smooth management of organisations (Hylko, 2005). Employers, however, are often unaware of who possesses expertise, or the nature of that expertise. The loss will be accentuated as members of the post-World War II baby boom cohort retire. Approaches to recover or recreate knowledge after it is lost are not sustainable in terms of prudent knowledge management. Organisations need to develop a deeper understanding of where expertise resides and how it is retained. This paper, presenting a limited set of results from a larger study, addresses the knowledge retention processes of an individual expert providing technical advice on a New Zealand construction industry helpline, in a leading scientific research organisation. Within the organisation, a single expert who possessed much personally-held undocumented knowledge was identified. Through detailed observations and peer interviews, the researchers learned much about the elements of his expertise, problem-solving processes and knowledge retention behaviour.