  The spectrum of Prokushkin--Vasiliev Theory is puzzling in light of the
Gaberdiel--Gopakumar conjecture because it generically contains an additional
sector besides higher-spin gauge and scalar fields. We find the unique
truncation of the theory avoiding this problem to order 2 in perturbations
around AdS$_3$. The second-order backreaction on the physical gauge sector
induced by the scalars is computed explicitly. The cubic action for the
physical fields is determined completely. We comment on a different higher-spin
theory without such additional fields at $\lambda=1$.
