  The gravitational dual to the grand canonical ensemble of a large $N$
holographic theory is a charged black hole. These spacetimes -- for example
Reissner-Nordstr\"om-AdS -- can have Cauchy horizons that render the classical
gravitational dynamics of the black hole interior incomplete. We show that a
(spatially uniform) deformation of the CFT by a neutral scalar operator
generically leads to a black hole with no inner horizon. There is instead a
spacelike Kasner singularity in the interior. For relevant deformations, Cauchy
horizons never form. For certain irrelevant deformations, Cauchy horizons can
exist at one specific temperature. We show that the scalar field triggers a
rapid collapse of the Einstein-Rosen bridge at the would-be Cauchy horizon.
Finally, we make some observations on the interior of charged dilatonic black
holes where the Kasner exponent at the singularity exhibits an attractor
mechanism in the low temperature limit.
