"The Frog's Legacy" is the sixth Christmas special episode of the BBCsitcom, Only Fools and Horses. It was first broadcast on 25 December 1987. In the episode, the Trotters search for the hidden gold legacy of Freddie "the Frog" Robdal, an old friend of their mother's.
It transpires that Del and Rodney's mother met Robdal and "befriended" him (a euphemism for Del's mother having had a brief affair with him, as was revealed she had done many times with a number of men throughout the series' development) before Rodney was born and while she and her husband Reg were having marital troubles. Renee describes Robdal as a very cultured man, into French wine and paintings. Robdal and his gang broke into a bank in London and stole £250,000 in gold bullion; the rest of the gang were apprehended by the Police, but Robdal escaped with the gold and hid it. It is on this information that Del embarks on a mission to find the lost gold, having inherited it from his mother on her death, who in turn, had had it bequeathed to her by Robdal in his will.
Uncle Albert, who knew Robdal vaguely during the war, finishes the tale later in the episode by stating that shortly after stealing the gold, and whilst still on the run from the Police, Robdal and an explosives expert known as "Jelly" Kelly, robbed a Post Office. During the robbery, Robdal inadvertently sat on a detonator, killing them both. Del mentions that he heard that Robdal had an affair with a married woman who lived on the estate and wonders why he left everything to Del and Rodney's mother. He also mentions a rumour that Robdal had an illegitimate child by that woman who would approximately be Rodney's age now. The throwaway remark begins to worry Rodney about the possibility that he may very well be that child, though Albert dismisses it as a rumour.
During the course of the story, Del gets Rodney a new job, though he declines to mention that it is working for the local funeral directors as a chief mourner, a fact Rodney does not take kindly to when he finds out. While arguing with Del, he accidentally leads the hearse down a one-way street. However, through his job there Rodney finds out that Robdal purchased a coffin from Rodney's employers when they first started business for a "friend" named "Alfred Broderick". Rodney quickly deduces that "Alfred Broderick" is an anagram of "Frederick Robdal", implying that Broderick did not exist, and that Robdal had purchased the coffin to hide the gold in and had arranged a fake funeral for it to be buried. While attempting to sell a faulty computer to the priest who married Andy and Lisa, Del learns that the same priest also buried "Mr Broderick". He then finally learns of the gold's whereabouts.
Having failed to mention it earlier, Albert confirms that Robdal earned the nickname "The Frog" because he was a frogman in the Royal Navy. Consequently, he buried the gold at sea to hide it from the authorities and intended to recover it at an opportune moment, but was killed before he could do so. While Del vows to find the gold, Rodney once again asks Albert about his resemblance to Robdal; Albert just dismisses it as rumours, but does acknowledge that he and Robdal do look a bit alike. Rodney then surmises, "Freddie the Frog. Killed himself by sitting on someone else's detonator. What a plonker."
This is the second occasion in the show's history that the issue of whether or not Rodney and Del share the same father is raised. It had previously been brought up in "Thicker than Water" when their estranged father Reg tricked them into believing that Del was not his son — though this was later exposed as a result of troublemaking on his part. Although Albert assures Rodney that the suggestion that he was fathered by Freddie Robdal were just rumours, "Sleepless in Peckham" settles the issue that Freddie was Rodney's father, and this is further confirmed in the 2010 prequel series Rock & Chips, in which Freddie (played by Nicholas Lyndhurst) has an affair with Del's mother before Rodney was born. It was suggested in a BBC interview with writer John Sullivan that it was intended that the reappearance of Robdal would signal the end of the show, but he decided against it and wrote Robdal into the series as already dead. "Sleepless in Peckham" would also establish that Del, as a young man, only ever knew Robdal as "Uncle Fred", which explained why Del was unfamiliar with Robdal's real name until Uncle Albert drunkenly told him the truth about Robdal's past with the Trotters.
This Christmas special marked the end of an era for the show, both in front of and behind the cameras. Ray Butt, who had been the show's producer since it started in 1981, decided to leave the BBC shortly after filming was complete. The day before he left, Butt told John Sullivan that he should seriously consider letting the series end with this episode; Butt felt that the series had run its course, and pointed to the disastrous reception of the previous year's Christmas special, "A Royal Flush" as proof of his point. Sullivan gave thought to Butt's words, but after "The Frog's Legacy" received a much more positive reception than "A Royal Flush" had done, decided to continue the series. However, Sullivan shared Butt's concerns that the series' format was starting to become stale, and so starting with the next Christmas special, "Dates," the series would maintain a balance between Del's get-rich-quick schemes and the personal lives of the Trotter Family.