We present high-spatial resolution imaging obtained with the Submillimeter Array (SMA) at 880 mu m and the Keck adaptive optics (AO) system at the K-S-band of a gravitationally lensed submillimeter galaxy (SMG) at z = 4.243 discovered in the Herschel Astrophysical Terahertz Large Area Survey. The SMA data (angular resolution approximate to 0.'' 6) resolve the dust emission into multiple lensed images, while the Keck AO KS-band data (angular resolution approximate to 0.'' 1) resolve the lens into a pair of galaxies separated by 0.'' 3. We present an optical spectrum of the foreground lens obtained with the Gemini-South telescope that provides a lens redshift of z(lens) = 0.595 +/- 0.005. We develop and apply a new lens modeling technique in the visibility plane that shows that the SMG is magnified by a factor of mu = 4.1 +/- 0.2 and has an intrinsic infrared (IR) luminosity of L-IR = (2.1 +/- 0.2) x 10(13) L-circle dot. We measure a half-light radius of the background source of r(s) = 4.4 +/- 0.5 kpc which implies an IR luminosity surface density of Sigma(IR) = (3.4 +/- 0.9) x 10(11) L-circle dot kpc(-2), a value that is typical of z > 2 SMGs but significantly lower than IR luminous galaxies at z similar to 0. The two lens galaxies are compact (r(lens) approximate to 0.9 kpc) early-types with Einstein radii of theta(E1) = 0.57 +/- 0.01 and theta(E2) = 0.40 +/- 0.01 that imply masses of M-lens1 = (7.4 +/- 0.5) x 10(10) M-circle dot and M-lens2 = (3.7 +/- 0.3) x 10(10) M-circle dot. The two lensing galaxies are likely about to undergo a dissipationless merger, and the mass and size of the resultant system should be similar to other early-type galaxies at z similar to 0.6. This work highlights the importance of high spatial resolution imaging in developing models of strongly lensed galaxies discovered by Herschel.