  An embedding of a unified dark sector model into string theory with the
following features is proposed: The model-independent axion descending from the
Kalb-Ramond 2-form field is identified with the dark-matter field, and the real
part of a K\"ahler modulus field -- the ``radius'' of one of the extra spatial
dimensions -- accounts for dark energy. The expectation value of the dilaton
field is stabilized by a gaugino condensation mechanism. A dark-energy
potential corresponding to a realistic low energy scale results from some
gentle tuning of the stabilized expectation value of the dilaton. The resulting
potential reproduces the one in a previous dark-sector model proposed by two of
us.
