  We present a detailed analysis and interpretation of the high-mass binary
V380 Cyg, based on high-precision space photometry gathered with the Kepler
space mission as well as high-resolution ground-based spectroscopy obtained
with the HERMES spectrograph attached to the 1.2m Mercator telescope. We derive
a precise orbital solution and the full physical properties of the system,
including dynamical component mass estimates of 11.43+/-0.19 and 7.00+/-0.14
solar masses for the primary and secondary, respectively. Our frequency
analysis reveals the rotation frequency of the primary in both the photometric
and spectroscopic data and additional low-amplitude stochastic variability at
low frequency in the space photometry with characteristics that are compatible
with recent theoretical predictions for gravity-mode oscillations excited
either by the convective core or by sub-surface convective layers. Doppler
Imaging analysis of the silicon lines of the primary suggests the presence of
two high-contrast stellar surface abundance spots which are located either at
the same latitude or longitude. Comparison of the observed properties of the
binary with present-day single-star evolutionary models shows that the latter
are inadequate and lack a serious amount of near-core mixing.
