  Extending our previous results on trans-Planckian ($Gs \gg \hbar$) scattering
of light particles in quantum string-gravity we present a calculation of the
corresponding S-matrix from the region of large impact parameters ($b \gg
G\sqrt{s}>\lambda_s$) down to the regime where classical gravitational collapse
is expected to occur. By solving the semiclassical equations of a previously
introduced effective-action approximation, we find that the perturbative
expansion around the leading eikonal result diverges at a critical value $b =
b_c = O(G\sqrt{s})$, signalling the onset of a new (black-hole related?)
regime. We then discuss the main features of our explicitly unitary S-matrix --
and of the associated effective metric -- down to (and in the vicinity of) $b =
b_c$, and present some ideas and results on its extension all the way to the $
b \to 0$ region. We find that for $b<b_c$ the physical field solutions are
complex-valued and the S-matrix shows additional absorption, related to a new
production mechanism. The field solutions themselves are, surprisingly,
everywhere regular, suggesting a quantum-tunneling -- rather than a
singular-geometry -- situation.
