Thingumajig The Avengers : Season 7 Episode 27

The vicar of a Norman church asks the Avengers' help when a team of archaeologists excavating a site underneath the church are all killed and their bodies rendered completely devoid of any energy. This is due to a little black box which sends out deadly charges of electricity. Furthermore its charges are nurturing a race of thingumajigs, pure energy creatures which will eat anything and must be stopped before they do great harm.