On March 31, 2001 at ~0635 UT when the CLUSTER constellation was near local midnight and at ~4 RE geocentric distance, sensors observed an energetic electron injection event associated with a strong (AE ~ 1200 nT) magnetospheric substorm. Geostationary spacecraft 1991-080 located at ~20 LT also saw an abrupt electron injection event at ~0630 UT and FAST spacecraft instruments (~19 LT) detected a powerful set of magnetic field, electric field, and energetic plasma signatures at ~0637 UT. The energetic neutral atom imaging experiments onboard the IMAGE spacecraft detected an injection of substorm-produced ions in the pre-midnight sector commencing at ~0630 UT. Electron injection signatures at the four separate CLUSTER locations allow us to infer the location, speed, and direction of the substorm injection boundary. Hence, the CLUSTER (and IMAGE) telescope-microscope combination is a long-sought realization of a major magnetospheric research objective and shows the power of localized multi-point measurements from CLUSTER.