Mathematics education is a high-stakes indicator of success in 'über' performative systems. The search to address England's mathematics underperformance resulted in cross-national attraction toward, and policy borrowing of, 'teaching for mastery' from the high-performing education systems of Shanghai and Singapore. We argue that the cultural baggage implicit in mastery was in direct conflict with fundamental structures underpinning the English education system--structures which resulted in significant barriers toward implementing and internalising mastery. Theoretically grounded in the work of Lyotard, Foucault, and Ball, our paper maps how teachers working in the East Midlands region of England borrowed, implemented, and internalised mastery. Our micro, classroom-scale, examination reveals macro-scale performative drivers, as well as the pitfalls of policy borrowing without due care and attention. We highlight that policy borrowing is far more complex than simply copying and checking for fidelity between the original and the borrowed. We conclude by suggesting that underestimating the consequences of policy borrowing has highly significant and even detrimental outcomes at both the micro and macro scales.