Every season there is an episode called "C.A.K.E.D." (i.e. C.A.K.E.D.-T.W.O., C.A.K.E.D.-T.H.R.E.E., etc.) with the exception being Season 6's episode; which is just S.I.X. The first C.A.K.E.D. episode, Operation: C.A.K.E.D., was the first episode of Codename: Kids Next Door. Operations C.A.K.E.D.-F.O.U.R. and C.A.K.E.D.-F.I.V.E. are double-length episodes, while S.I.X. is the first (and since the show stops production at the end of the 6th season, the only one) to not have the word "C.A.K.E.D." in it.
The plot revolves around the Delightful Children from Down the Lane not sharing their birthday cake (and for the first three episodes making kids watch them eat it) and Sector V trying to stop them. The plot was altered a bit after the first three episodes. The sixth episode was unknown to be involved with the DCFDTL's cake until the end. The last episode, I.N.T.E.R.V.I.E.W.S., was loosely based on a CAKED episode. All the birthdays happen in a year. It is mentioned in caked five that they have five birthdays a year.
References to Popular Culture
In Operation E.N.G.L.A.N.D, one of the KND operatives wears an overcoat and scarf very similar to the Fourth Doctor's.
In Operation E.N.G.L.A.N.D, the one blonde non-KND kid parodies the Nudge Nudge skit from Monty Python's Flying Circus with Nigel. (One could argue that the whole tavern scene was one big parody of British English in general).
In Operation G.I.R.L.F.R.I.E.N.D., Number One said that he thought that the members of the splinter cell were those geeks who watch Doctor Space Time and the Continuums.
Trivia
Operation: I.N.T.E.R.V.I.E.W.S. is a one-hour feature[1], which premiered on December 29, 2007 in the Philippines, and January 21, 2008 in the United States and aired on February 29, 2008 in Australia, and also aired on Sunday 2nd March 2008 in the UK.