David Tennant as Buck Douglas (2016-2017-Alien Alert only)
All S1
S1 E15Unfinished Business
John Barrowman as Flex Dexter (2018-Set for Action! only)
Kerry Shale as Don Sledgehammer (2018-Set for Action! only) and Dr. Crumpton (2020-Norman Price and the Mystery of the Sky only)
Colin McFarlane as PC Malcolm Williams (2020-present)
Sasha Behar as Sgt. Rose Ravani (2020-Norman Price and the Mystery of the Sky only)
Denise Van Outen as Professor Polonium (2020-Norman Price and the Mystery of the Sky only)
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