  We analyze (2+1)-dimensional gravity with a Chern--Simons term and a negative
cosmological constant, primarily at the weak field level. The full theory is
expressible as the sum of two higher derivative SL(2,R) "vector" Chern-Simons
terms, while the physical bulk degrees of freedom correspond to a single
massive scalar field, just as for Lambda=0. The interplay of Lambda and the
mass parameter mu can be studied, and any physical mass--including the
conformal value with null propagation--is accessible by tuning mu. The single
bulk mode yields a complete set of normalizable positive energy wave packets,
as long as one chooses the usual, "wrong" sign of G necessary to connect
smoothly with the known Lambda=0 limit. The chiral Chern--Simons coupling leads
to gauge invariant linearized curvatures propagating with chirality-dependent
masses. Linearized metric fluctuations have a finite asymptotic
Fefferman--Graham expansion about the Poincar'e metric for any mass value
greater or equal to a "critical" one, where various amusing effects appear,
such as vanishing of one of the two "vector" Chern-Simons terms and an
equivalence between tensor and vector excitations. We also find a set of
chiral, pp-wave metrics that exactly solve the full nonlinear equations.
