- We present HST WFC3-IR imaging in the fields of six apparently-bright Dusty Star Forming Galaxies (DSFGs) at z = 2-4 identified by their rest-frame far-infrared colors using the Planck and Herschel space facilities. We detect near-infrared counterparts for all six submillimeter sources, allowing us to undertake strong lensing analyses. One field in particular stands out for its prominent giant arcs, PLCK G165.7+67.0 (G165). After combining the color and morphological information, we identify eleven sets of image multiplicities in this one field. We construct a strong lensing model constrained by this lensing evidence, which uncovers a bimodal spatial mass distribution, and from which we measure a mass of 2.6(+/- 0.11) x 10^14 Msun within ~250 kpc. The bright (S_350 ~ 750 mJy) DSFG appears as two images: a giant arc with a spatial-extent of 4.5 arcsec that is merging with the critical curve, and a lower magnification counter-image that is detected in our new longer wavelength ground- and space-based imaging data. Using our ground-based spectroscopy, we calculate a dynamical mass of 1.3(+0.04/-0.70) x 10^15 Msun to the same fixed radius, although this value may be inflated relative to the true value if the velocity distribution is enhanced in the line-of-sight direction. We suggest that the bimodal mass taken in combination with the weak X-ray flux and low Sunyaev-Zel'dovich effect decrement may be explained as a pre-merger for which the intra-cluster gas is diluted along the line-of-sight, while the integrated surface mass density is supercritical to strong lensing effects.