In a sly reference to crew member, at the beginning of Act IV (at around 40 minutes), Michael Tressider is taken to an Invaders laboratory disguised as a company called Sletnir Chemicals. "Sletnir" spelled backwards is "Rintels"--and is the last name of associate producer David W. Rintels.
David Vincent tells Michael Tressider, "The country's largest defense contractor doesn't go around acting like a gangster out of The Untouchables." Quinn Martin was Executive Producer of both The Invaders (1967) and The Untouchables (1959). William Windom was NOT one of the over 100 actors and staff that worked on both shows.
William Windom appeared earlier in the series, Doomsday Minus One (1967) where he played Major Rick Graves.
At the beginning when Michael Tressider speaks to Vincent he mentions an industrial sabotage event "last year". This vague reference apparently refers to season one, but which one isn't clear, since this is the only time Tressider appears. There was one story this might refer to, entitled "Vikor", which happened to guest star Diana Hyland.
The actor who portrays the Lieutenant is Martin West, who replaced Roy Thinnes in the role of Dr. Phil Brewer on General Hospital (1963).