Organizations developing safety-critical software are increasingly seeking to create better practices by meshing agile and plan-driven development processes. Significant differences between the agile and the plan-driven processes make meshing difficult, and very little empirical evidence on using agile processes for safety-critical software development exists. There are four areas of concern, in particular, for meshing the development of safety-critical software concerning: documentation, requirements, life cycle and testing. We report on a case study of a pharmaceutical organization in which a Scrum process was implemented to support agile software development in a plan-driven safety-critical project. The purpose was to answer the following research question: For safety-critical software, what can a software team do to mesh agile and plan-driven processes effectively? The main contribution of the paper is an elaborated understanding of meshing in the four areas of concern and how the conditions for safety-critical software influence them. We discuss how meshing within the four areas of concern is a contribution to existing research.