We give the first rigorous derivation of a kinetic equation in a nontrivial translation invariant situation. We consider the heavy particle (mass scaled as $m\epsilon^{-\delta},\delta\ge 0$) in the ideal fermi gas with translation invariant interaction $\epsilon V$ between them. In the Heisenberg representation we prove convergence to the strongly continuous completely-positive semigroup $T_s$ for any value of scaled time $s$, $t=s/\epsilon^2$ and for $\delta>2$. When $\delta=2$ $T_s$ is not a semigroup. For $2> \delta\ge 0$ we announce some more weak results.