From what I gather, Martha Plimpton met River Phoenix through Joaquin Phoenix and/or Corey Feldman, who had both acted
with these two. They acted together twice, first in the movie The Mosquito Coast
, then two years later in Running On Empty
. Martha then accompanied River to the academy awards and they dated for quite some time. It is said that they broke up because
of Martha's anti-drug stance, but it is also said that River admitted before he died that Martha was his soul mate.