  We investigate the $R_b$--$R_c$ problem, starting from the more diffcult
$R_c$. Introducing an isosinglet charge 2/3 quark $Q$ moves both $R_c$ and
$R_b$ in the right direction. If one allows for large $c$-$Q$ {\it and} $t$-$Q$
mixings, then $R_c$ could be reduced because of singlet content of charm quark,
while $R_b$ gets enhanced by a light effective top quark mass in the loop. The
heavy quark observed at CDF would be dominantly a singlet quark, while the top
quark is lighter than $M_W$. It is necessary to introduce a second Higgs
doublet, where $H^+$ is heavy while at least one exotic neutral Higgs boson is
very light. $H^+$--$h^0$ splitting accounts for $\delta\rho$, while light $h^0$
induce fast $t\to c + h^0$ decay and hides the actual top quark at the
Tevatron. The scenario can be immediately tested at LEP II via search for light
top production (and toponium!). At Tevatron, one should search for exotic decay
modes such as $Q\to Z + X$ or $Q\to H + X$, or measure the BR for the standard
$bW$ mode. Light top search should also be renewed.
