The interaction between an interplanetary shock and the earth's magnetosphere was observed by ISEE-1 and -2 on August 27, 1978. The two spacecraft were initially inside and near the nose of the magnetosphere, separated by about 1000 km. The shock, identified by ISEE-3, reached the vicinity of the earth in approximately half an hour. As a result of the interaction the magnetospheric boundaries moved rapidly earthward, so that in less than three minutes both the magnetopause and the bowshock passed over the ISEE-2 and -1 spacecraft. Time delays between the two spacecraft yielded a boundary speed of 195 km/sec for the magnetopause. This exceptionally large speed provided a rapid scan of the boundary at the time and place of observation, but important differences in boundary structure existed in data taken 5 seconds apart by the two spacecraft. A rotational MHD wave seemed present during the ISEE-2 crossing and absent during the ISEE-1 crossing. The magnetopause thickness was found to be 860 Km at ISEE-2, and 780 km at ISEE-1. The data indicated boundary structure on a scale of 370 km or less, and/or high frequency (? 0.21 Hz) large amplitude temporal variations. These results are inconsistent with steady state reconnection but are compatible with localized patchy reconnection.