  We study a string theory which is exclusively based on extrinsic curvature
action. It is a tensionless string theory because the action reduces to
perimeter for the flat Wilson loop. We are able to solve and quantize this
high-derivative nonlinear two-dimensional conformal field theory. The absence
of conformal anomaly in quantum theory requires that the space-time should be
13-dimensional. We have found that all particles, with arbitrary large spin,
are massless. This pure massless spectrum is consistent with the tensionless
character of the theory and we speculate that it may describe unbroken phase of
standard string theory.
