Dusty star-forming galaxies (DSFGs) detected at $z > 4$ provide important examples of the first generations of massive galaxies. However, few examples with spectroscopic confirmation are currently known, with Hershel struggling to detect significant numbers of $z > 6$ DSFGs. NGP6_D1 is a bright 850 $mu m$ source (12.3 $pm$ 2.5 mJy) with no counterparts at shorter wavelengths (a SPIRE dropout). Interferometric observations confirm it is a single source, with no evidence for any optical or NIR emission, or nearby likely foreground lensing sources. No $>3sigma$ detected lines are seen in both LMT RSR and IRAM 30m EMIR spectra of NGP6_D1 across 32 $GHz$ of bandwidth despite reaching detection limits of $sim 1 mJy/500 km~s^{-1}$, so the redshift remains unknown. Template fitting suggests that NGP6_D1 is most likely between $z = 5.8$ and 8.3. SED analysis finds that NGP6_D1 is a ULIRG, with a dust mass $sim 10^8$ - $10^9$ $M_{odot}$ and a SFR of $sim$ 500 $M_{odot}~yr^{-1}$. We place upper limits on the gas mass of NGP6_D1 of $M_{H2}$ $ < (1.1~pm~3.5) times 10^{11}$ $M_{odot}$, consistent with a gas-to-dust ratio of $sim$ 100 - 1000. We discuss the nature of NGP6_D1 in the context of the broader submm population, and find that comparable SPIRE dropouts account for $sim$ 20% of all SCUBA-2 detected sources, but with a similar flux density distribution to the general population.
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