  This paper presents a photometric and spectroscopic study of the short-period
binary star
  Cl*~Melotte~111~AV~1224. Measurements in the $B$, $V$, and $R$ passbands
obtained during three observing runs
  between 2014 and 2017 and medium-resolution spectra secured in 2014, are
analyzed together with public data from
  the SuperWASP and LAMOST projects. Our light curves show marked asymmetry
with a variable O'Connell effect. The SuperWASP photometry
  is used to derive a mean binary period of 0.345225 days.
  The analysis of the $(O-C)$ diagram reveals that the orbital period is
decreasing at a rate of $dP/dt = -3.87 \times 10^{-6}$ days yr$^{-1}$, which
  may be caused by mass transfer from the more-massive component to the
less-massive one.
  The system is found to be a single-lined spectroscopic binary with a systemic
velocity, $\gamma = 1 \pm 3$ Km s$^{-1}$, and a semi-amplitude, K$_{1}$ = 21
$\pm$ 5 Km s$^{-1}$. The spectral classification and the effective temperature
of the primary component are estimated to be K0V $\pm$ 1 and $5200 \pm 150$ K,
respectively. The photometric and spectroscopic solutions reveal that
Cl*~Melotte~111~AV~1224 is a low-mass ratio ($q=m_{2}/m_{1} \sim 0.11$),
low-inclination ($\sim ~ 38^{\circ}$) near-contact system. The masses, radii
and luminosity for the primary and secondary are estimated to be $1.02 \pm
0.06\, M_\odot$, $1.23 \pm 0.05\, R_\odot $, $1.01 \pm 0.06\, L_\odot$ and
$0.11 \pm 0.08\, M_\odot$, $0.45 \pm 0.05\, R_\odot$, $0.10 \pm 0.06\,
L_\odot$, respectively. The marginal contact, together with the period
decrease, suggests that this binary system may be at a key evolutionary stage,
as predicted by the theory of thermal relaxation oscillations.
