We first discovered the presence of a particularly massive cloud in the neighborhood of the Sun, close to the Galactic plane in the direction of Perseus, toward l = 150 deg, b = -10 deg, using interstellar absorption by the 7699 A resonance line of K I (Trapero et al. 1992). In the present investigation we show the results of mapping the cloud in the 21 cm line of H I, supplemented by further K I observations. This combination is particularly effective, since the K I observations give us distances, within close limits, and accurate velocities of the single strong interstellar component detected along each line of sight, which enables us to identify the cloud as seen in absorption in the H I spectra, from among many emission components due to more distant clouds in the plane. The absorption spectra in H I at 21 cm can then be used to find temperatures and to carry out more comprehensive mapping than using K I. We find that the cloud has kinetic temperatures going down to 30 K, densitites in the range up to 70/cu cm, a diameter of approximately 15 pc, and a mass of some 1300 solar mass. The cloud is a good candidate to contain a molecular core.