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We propose multi-epoch STIS FUV spectroscopy of the only Be star + black hole binary candidate comma MWC 656. These observations will reveal the nature of the Be star.s elusive companiondoublePoint a black hole comma or an intermediate-mass (virgul3 Msun) stripped helium star. Either scenario would be extraordinarydoublePoint intermediate-mass stripped stars are the main progenitors of stripped-envelope supernovae comma X-ray binaries comma and merging neutron stars comma yet they have remained elusive for decades the black hole would be in the mass gap and would be the only known X-ray faint high-mass X-ray binary containing a black hole. Our proposed observations will unambiguously distinguish between these two scenarios comma as the UV spectrum of a massive stripped star will be very different from that of a black hole accretion disk. FUV spectra will also constrain the spectral type comma mass comma and RV variability of the Be star more reliably than has been possible with optical data comma which are strongly contaminated by the Be star.s circumstellar disk.