  We study superstring theory in three dimensional Anti-de Sitter spacetime
with NS-NS flux, focusing on the case where the radius of curvature is equal to
the string length. This corresponds to the critical level k=1 in the
Wess-Zumino-Witten description. Previously, it was argued that a transition
takes place at this special radius, from a phase dominated by black holes at
larger radius to one dominated by long strings at smaller radius. We argue that
the infinite tower of modes that become massless at k=1 is a signal of this
transition. We propose a simple two-dimensional conformal field theory as the
holographic dual to superstring theory at k=1. As evidence for our conjecture,
we demonstrate that at large N our putative dual exactly reproduces the full
spectrum of the long strings of the weakly coupled string theory, including
states unprotected by supersymmetry.
