Del Boy, Rodney and Albert travel to Hampshire to attend the wedding of Trigger's niece, Lisa, who appeared in the episode "Tea for Three".
Whilst there, Trigger's Aunt Reenie Turpin (Joan Sims) informs Del about a Peckham-based gentleman thief, Freddie "The Frog" Robdal, from the early 1960s.
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.
However, through his job at the undertakers, Rodney finds out that Robdal purchased an extra large coffin from them in 1963 for a friend named Alfred Broderick.
Having failed to mention it earlier, Albert confirms that Robdal earned the nickname "The Frog" because he was a frogman in the Royal Navy.
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 show.