We report ground-based follow-up observations of the exceptional source, ID 141, one of the brightest sources detected so far in the Herschel Astrophysical Terahertz Large Area Survey cosmological survey. ID 141 was observed using the IRAM 30 m telescope and Plateau de Bure interferometer (PdBI), the Submillimeter Array, and the Atacama Pathfinder Experiment submillimeter telescope to measure the dust continuum and emission lines of the main isotope of carbon monoxide and carbon ([C I] and [C II]). The detection of strong CO emission lines with the PdBI confirms that ID 141 is at high redshift (z = 4.243 +/- 0.001). The strength of the continuum and emission lines suggests that ID 141 is gravitationally lensed. The width (Delta V(FWHM) similar to 800 km s(-1)) and asymmetric profiles of the CO and carbon lines indicate orbital motion in a disk or a merger. The properties derived for ID 141 are compatible with an ultraluminous (L(FIR) similar to (8.5 +/- 0.3) x 10(13) mu(-1)(L) L(circle dot), where mu L is the amplification factor), dense (n approximate to 10(4) cm(-3)), and warm (T(kin) approximate to 40 K) starburst galaxy, with an estimated star formation rate of (0.7-1.7) x 10(4) mu(-1)(L) M(circle dot) yr(-1). The carbon emission lines indicate a dense (n approximate to 10(4) cm(-3)) photon-dominated region, illuminated by a far-UV radiation field a few thousand times more intense than that in our Galaxy. In conclusion, the physical properties of the high-z galaxy ID 141 are remarkably similar to those of local ultraluminous infrared galaxies.