Lt. Ayshea Johnson (Ayshea Brough) becomes S.H.A.D.O.'s communications officer following the departure of Keith Alexander (L.t Ford) from the series after the production break.
This was the third episode broadcast, but the nineteenth to be filmed.
This is Wanda Ventham's (Colonel Lake) return to the series for the last eight episodes after only being seen in the pilot episode "Identified". Ventham took over the post of S.H.A.D.O.'s first officer, replacing George Sewell (Colonel Freeman), who left UFO following the change of studios, being later unavailable when series production resumed at Pinewood Studios.
First episode in broadcast order to introduce ground defence system vehicles on the Moon. These large vehicles with caterpillar treads are capable of firing missiles from the lunar surface.
Lt. Regan has a number of nervous habits. Watch his hands as he pilots his interceptor and when he enters the rec room.