The lead characters are ex-astronaut Jeff Tracy, founder of International Rescue, and his five adult sons, who pilot the organisation's primary vehicles: the Thunderbird machines.
In "Desperate Intruder", the organisation is forced into action to save two of its own members when Brains and Tin-Tin (voiced by David Graham and Christine Finn) are attacked by The Hood during an archaeological expedition in search of lost treasure.
[2] Brains and Tin-Tin depart for the Middle East[1] to conduct an archaeological survey at Lake Anasta, which contains a submerged temple believed to harbour lost treasure.
On Tracy Island, Jeff is concerned by the loss of radio contact with Brains and Tin-Tin and sends out Scott, Virgil and Gordon in Thunderbirds 1 and 2 to investigate.
Scott discovers that Thunderbird 1's camera detector has been active, prompting Brains to realise that their attacker has been using the expedition as bait to lure International Rescue into a trap.
Desperate to make amends for the trouble, he dives back to the temple alone to recover more treasure, unaware that The Hood has rigged the area with intruder alarms and explosive charges.
[6] Rating the episode four out of five, Tom Fox of Starburst magazine writes that "Desperate Intruder" emphasises The Hood's "venal" and cruel nature, adding that the negative "stock stereotype" that he represents is redeemed by the "sheer silliness of [his] hypnotising naughtiness".
[7] Describing the story as a "straightforward yarn" about lost treasure, Marcus Hearn states that Robertson's script "chooses to ignore" many of Thunderbirds' key themes, noting that the customary "emphasis on technology and engineering [...] is almost entirely missing here."