  We report deep spectroscopy of ten planetary nebulae (PNe) in the Andromeda
Galaxy (M31) using the 10.4m GTC. Our targets reside in different regions of
M31, including halo streams and dwarf satellite M32, and kinematically deviate
from the extended disk. The temperature-sensitive [O III] 4363 auroral line is
observed in all targets. For four PNe, the GTC spectra extend beyond 1 micron,
enabling explicit detection of the [S III] 6312 and 9069,9531 lines and thus
determination of the [S III] temperature. Abundance ratios are derived and
generally consistent with AGB model predictions. Our PNe probably all evolved
from low-mass (<2 M_sun) stars, as analyzed with the most up-to-date post-AGB
evolutionary models, and their main-sequence ages are mostly ~2-5 Gyr. Compared
to the underlying, smooth, metal-poor halo of M31, our targets are uniformly
metal-rich ([O/H]> -0.4), and seem to resemble the younger population in the
stream. We thus speculate that our halo PNe formed in the Giant Stream's
progenitor through extended star formation. Alternatively, they might have
formed from the same metal-rich gas as did the outer-disk PNe, but was
displaced into their present locations as a result of galactic interactions.
These interpretations are, although speculative, qualitatively in line with the
current picture, as inferred from previous wide-field photometric surveys, that
M31's halo is the result of complex interactions and merger processes. The
behavior of N/O of the combined sample of the outer-disk and our
halo/substructure PNe signifies that hot bottom burning might actually occur at
<3 M_sun, but careful assessment is needed.
