  We report the detection of Lyman Continuum (LyC) emission from the galaxy,
CDFS-6664, at z=3.797 in a sample of Lyman break galaxies with detected [OIII]
emission lines. The LyC emission is detected with a significance ~$5\sigma$ in
the F336W band of the Hubble Deep UV Legacy Survey, corresponding to the
650-770 Angstrom rest-frame. The light centroid of the LyC emission is offset
from the galaxy center by about 0.2" (1.4 pkpc). The Hubble deep images at
longer wavelengths show that the emission is unlikely provided by low-redshift
interlopers. The photometric and spectroscopic data show that the possible
contribution of an active galactic nucleus is quite low. Fitting the spectral
energy distribution of this source to stellar population synthesis models, we
find that the galaxy is young (~50 Myr) and actively forming stars with a rate
of 52.1$\pm$4.9 $M_{\odot}\mathrm{yr^{-1}}$. The significant star formation and
the spatially offset LyC emission support a scenario where the ionizing photons
escape from the low-density cavities in the ISM excavated by massive young
stars. From the nebular model, we estimate the escape fraction of LyC photons
to be 38$\pm$7% and the corresponding IGM transmission to be 60%, which
deviates more than 3$\sigma$ from the average transmission. The unusually high
IGM transmission of LyC photons in CDFS-6664 may be related to a foreground
type-2 quasar, CDF-202, at z=3.7, with a projected separation of 1.2' only. The
quasar may have photoevaporated optically thick absorbers and enhance the
transmission on the sightline of CDFS-6664.
