We prove that the inertia groups of all sufficiently-connected, highdimensional (2n)-manifolds are trivial. Specifically, for m 0 and k > 5/12, suppose M is a (km)-connected, smooth, closed, oriented m-manifold and Σ is an exotic m-sphere. We prove that, if M Σ is diffeomorphic to M , then Σ bounds a parallelizable manifold. Our proof is an application of higher algebra in Pstragowski's category of synthetic spectra, and builds on previous work of the authors. Contents 1. Introduction 1 2. The geometry of inertia groups 4 3. The bar spectral sequence approach to the unit of MO n 5 4. Additional background 8 5. Bounding Adams filtrations with synthetic lifts 13 6. Applications of vanishing lines 17 References 19