  Recently proposed "multicritical" higher-derivative gravities in Anti de
Sitter space carry logarithmic representations of the Anti de Sitter isometry
group. While generically non-unitary already at the quadratic, free-theory
level, in special cases these theories admit a unitary subspace. The simplest
example of such behavior is "tricritical" gravity. In this paper, we extend the
study of parity-even tricritical gravity in d = 3, 4 to the first nonlinear
order. We show that the would-be unitary subspace suffers from a linearization
instability and is absent in the full non-linear theory.
