Player engagement with video games is widely discussed. The apparently contrasting phenomenon of frustration is less widely researched. Frustration is reported to impede player engagement but it is unlikely that a game which never frustrated at all would be enjoyable. In that context, further work is needed to identify, understand and model the character, timing and context of frustrations which help rather than hinder a positive gaming experience. This paper investigates the relationship between frustration and engagement over time in a carefully selected video game. We find that engagement often falls as frustration rises (and vice versa) but also report upon situations in which a rise in frustration can give rise to an increase in engagement. We consider the implications of these results for both game developers and the wider community of HCI researchers interested in gamification and user engagement.