  We present our analysis of the theory constructed in 1965 by Ogievetsky and
Polubarinov (OP) -- the first ever theory of interacting massive gravitons. Its
mass term is adjusted in such a way that the non-linear field equations imply
as a consequence the linear Hilbert-Lorentz condition, which restricts the spin
of states in the theory. Strikingly, for special parameter values this theory
coincides with one of the "ghost-free" massive gravity models rediscovered only
in 2010. For generic parameter values, however, it propagates 6 degrees of
freedom and shows ghost around flat space. Surprizingly, we find that the de
Sitter space remains stable for a large region of the parameter space, provided
that the Hubble expansion rate is large enough, hence the Boulware-Deser mode
is benign in this case. We study also other solutions and find that the Milne
universe -- a sector of Minkowski space -- is stable in the UV limit. This
presumably implies that at the non-linear level the ghost instability in flat
space develops only for long waves, similarly to the classical Jeans
instability.
