  We present the first results of a 4.5 year monitoring campaign of the three
bright images of multiply imaged $z=2.805$ quasar SDSS J2222+2745 using the
Gemini North Multi-Object Spectrograph (GMOS-N) and the Nordic Optical
Telescope (NOT). We take advantage of gravitational time delays to construct
light curves surpassing 6 years in duration and achieve average spectroscopic
cadence of 10 days during the 8 months of visibility per season. Using multiple
secondary calibrators and advanced reduction techniques, we achieve
percent-level spectrophotometric precision and carry out an unprecedented
reverberation mapping analysis, measuring both integrated and velocity-resolved
time lags for CIV. The full line lags the continuum by $\tau_{\rm cen} =
36.5^{+2.9}_{-3.9}$ rest-frame days. We combine our measurement with published
CIV lags and derive the $r_{\rm BLR}-L$ relationship $\log_{10}( \tau / {\rm
day}) = (1.00\pm 0.08) + (0.48\pm 0.04) \log_{10}[\lambda
L_\lambda(1350{\r{A}})/10^{44}~{\rm erg ~s}^{-1}]$ with 0.32$\pm$0.06 dex
intrinsic scatter. The velocity-resolved lags are consistent with circular
Keplerian orbits, with $\tau_{\rm cen} = 86.2^{+4.5}_{-5.0}$, $25^{+11}_{-15}$,
and $7.5^{+4.2}_{-3.5}$ rest-frame days for the core, blue wing, and red wing,
respectively. Using $\sigma_{\rm line}$ with the mean spectrum and assuming
$\log_{10} (f_{{\rm mean},\sigma}) = 0.52 \pm 0.26$, we derive
$\log_{10}(M_{\rm BH}/M_{\odot}) = 8.63 \pm 0.27$. Given the quality of the
data, this system represents a unique benchmark for calibration of $M_{\rm BH}$
estimators at high redshift. Future work will present dynamical modeling of the
data to constrain the virial factor $f$ and $M_{\rm BH}$.
