  This paper is an extended version of a talk at the conference Constrained
Dynamics and Quantum Gravity QG99. It reviews some work on the quantum collapse
of the spherically symmetric gravitating thin shell of zero rest mass. Recent
results on Kucha\v{r} decomposition are applied. The constructed version of
quantum mechanics is unitary, although the shell falls under its Schwarzschild
radius if its energy is high enough. Rather that a permanent black hole,
something like a transient black and white hole pair seems to be created in
such a case.
