Day of Disaster is the 15th produced, and the 6th broadcast, episode of the British television series Thunderbirds.
Brains is on something of a "busman's holiday" - he's in England, visiting Lady Penelope at her home, where they're watching TV coverage of the giant Martian Space Probe (MSP) as it's being transported to its future launch site.
As the rocket and its equally-massive transporter slowly traverse the Allington Suspension Bridge, however, the span - its structure stressed by an overnight thunderstorm - strains beneath the added weight - and suddenly gives way! Bridge, rocket and transporter head en masse for the drink - collapsing into the Allington River below. The MSP now sits on the river-bottom, buried under the massed debris of the bridge - and its automatic-countdown clock activated by the impact...and once it takes off, with its two-man crew still trapped inside, it will uncontrollably explode!
Brains is determined to get to the area - "I couldn't face the fellas back at the base, if I hadn't tried to do something!" And do something, he does...and one of International Rescue's strangest life-saving scenarios is in store...
Day of Disaster on Thunderbirds Wiki: http://thunderbirds.fandom.com/wiki/Day_Of_Disaster