Origin of quantum spin liquid phase in Ca$_{10}$Cr$_7$O$_{28}$

Ca$_{10}$Cr$_7$O$_{28}$ is a spin--1/2 magnet with a Kagom\'e--bilayer structure and complex competing interactions, which has recently been shown to support a quantum spin liquid state. In this talk we explore what can be learned about Ca$_{10}$Cr$_7$O$_{28}$ through a combination of analytic techniques, and classical Monte Carlo simulation. Despite the underlying complexity of the material, we find that the spin liquid in Ca$_{10}$Cr$_7$O$_{28}$ may admit of a deceptively simple explanation.