This seminar explores the pedagogical potential of investigating secondary school science curricula through the lens of the Threshold Concept Framework (TCF). A cohort of trainee secondary school science teachers in England worked collaboratively to co-construct their understanding of threshold concepts in A-level sciences based on their individual perceptions and experiences. Themes emerged which I argue to be inter-disciplinary Threshold Epistemes, concepts that are not the difficult content areas identified as troublesome but constitute more abstract ideas which are fundamental to thinking as a scientist within and across sub-disciplines. These are ways of understanding, and/or systems of ideas. Threshold Epistemes identified and discussed are: models, scale, randomness and language. I also further argue that the process of engaging with the TCF as a theoretical framework has potential to be pedagogically productive for teachers and pupils.