  We present a plausible counterexample to the weak cosmic censorship
conjecture in the four-dimensional Einstein-Scalar theory with asymptotically
flat boundary conditions. Our setup stems from the analysis of the massive
Klein-Gordon equation on a fixed Kerr black hole background. In particular, we
construct the quasinormal spectrum numerically, and analytically in the WKB
approximation, then go on to compute its backreaction on the Kerr geometry. In
the regime of parameters where the analytic and numerical techniques overlap we
find perfect agreement. We give strong evidence for the existence of a
nonlinear instability at late times.
