  We present a spectroscopic survey of candidate red giant branch stars in the
extended star cluster, EC4, discovered in the halo of M31 from our CFHT/MegaCam
survey, overlapping the tidal streams, Stream Cp and Stream Cr. These
observations used the DEep Imaging Multi-Object Spectrograph (DEIMOS) mounted
on the Keck II telescope to obtain spectra around the CaII triplet region with
~1.3 Angstroms resolution. Six stars lying on the red giant branch within 2
core-radii of the centre of EC4 are found to have an average
vr=-287.9^{+1.9}_{-2.4}km/s and velocity dispersion of 2.7^{+4.2}_{-2.7}km/s,
taking instrumental errors into account. The resulting mass-to-light ratio for
EC4 is M/L=6.7^{+15}_{-6.7}Msun/Lsun, a value that is consistent with a
globular cluster within the 1 sigma errors we derive. From the summed spectra
of our member stars, we find EC4 to be metal-poor, with [Fe/H]=-1.6+/-0.15. We
discuss several formation and evolution scenarios which could account for our
kinematic and metallicity constraints on EC4, and conclude that EC4 is most
comparable with an extended globular cluster. We also compare the kinematics
and metallicity of EC4 with Stream Cp and Stream Cr, and find that EC4 bears a
striking resemblance to Stream Cp in terms of velocity, and that the two
structures are identical in terms of both their spectroscopic and photometric
metallicities. From this we conclude that EC4 is likely related to Stream Cp.
