  We present Keck/KPIC high-resolution ($R\sim35,000$) $K$-band thermal
emission spectroscopy of the ultra-hot Jupiter WASP-33b. The use of KPIC's
single-mode fibers greatly improves both blaze and line-spread stabilities
relative to slit spectrographs, enhancing the cross-correlation detection
strength. We retrieve the dayside emission spectrum with a nested sampling
pipeline which fits for orbital parameters, the atmospheric
pressure-temperature profile, and molecular abundances.We strongly detect the
thermally-inverted dayside and measure mass-mixing ratios for CO ($\log\rm
CO_{MMR} = -1.1^{+0.4}_{-0.6}$), H$_2$O ($\log\rm H_2O_{MMR} =
-4.1^{+0.7}_{-0.9}$) and OH ($\log\rm OH_{MMR} = -2.1^{+0.5}_{-1.1}$),
suggesting near-complete dayside photodissociation of H$_2$O. The retrieved
abundances suggest a carbon- and possibly metal-enriched atmosphere, with a
gas-phase C/O ratio of $0.8^{+0.1}_{-0.2}$, consistent with the accretion of
high-metallicity gas near the CO$_2$ snow line and post-disk migration or with
accretion between the soot and H$_2$O snow lines. We also find tentative
evidence for $\rm ^{12}CO/^{13}CO \sim 50$, consistent with values expected in
protoplanetary disks, as well as tentative evidence for a metal-enriched
atmosphere (2--15$\times$ solar). These observations demonstrate KPIC's ability
to characterize close-in planets and the utility of KPIC's improved
instrumental stability for cross-correlation techniques.
