Jeff, Brains and Tin-Tin find themselves trapped onboard a crooked entrepreneur's automated cross-country monorail that is hurtling towards a collapsed bridge without means of stopping.
| Actor | Role |
|---|---|
 Peter DyneleyJeff Tracy / Hugo (voice) | Jeff Tracy / Hugo (voice) |
 Shane RimmerScott Tracy (voice) | Scott Tracy (voice) |
 David HollidayVirgil Tracy (voice) | Virgil Tracy (voice) |
 Matt ZimmermanAlan Tracy / Doolan / Stan (Patrol 304) / Patrol Base (voice) | Alan Tracy / Doolan / Stan (Patrol 304) / Patrol Base (voice) |
 David GrahamBrains / Parker / Warren Grafton / Harry Malloy (voice) | Brains / Parker / Warren Grafton / Harry Malloy (voice) |
 Sylvia AndersonLady Penelope (voice) | Lady Penelope (voice) |
 Christine FinnTin-Tin (voice) | Tin-Tin (voice) |
 Ray BarrettSelsden / 2nd Investor / Joe (Patrol 304) / Crook with Machine Gun (voice) | Selsden / 2nd Investor / Joe (Patrol 304) / Crook with Machine Gun (voice) |