Brink of Disaster
S1:E22
1966
IMDb
An unscrupulous investor attempts to recruit Lady Penelope into funding his automated, cross-country monorail building project. Jeff volunteers to ride the prototype, but he, Brains, and Tin-Tin find themselves trapped onboard, and with no possibility of escape, when it is discovered that the monorail train is speeding towards a stricken bridge.