SpongeBob is running towards Patrick's house, ready to go jellyfishing. Patrick says he'll go with him, but must put away his "secret box" first. SpongeBob asks him what's inside the box, but Patrick refuses to let SpongeBob see. Despite repeated attempts, SpongeBob is unable to get Patrick into opening the box, even after he tempts Patrick with secrets of his own. All that is known is that whatever is in the box is extremely funny. SpongeBob eventually gives up and decides not to look.
That night, SpongeBob finally snaps and sneaks into Patrick's house and tries to sneak a peek while Patrick sleeps. He makes several noises, but Patrick doesn't wake up. However, SpongeBob accidentally speaks, and Patrick wakes up and catches him in the act. He is shocked, and declares their friendship to be over. But, Patrick ultimately forgives him and opens the box. Inside, there is just a piece of string ("A secret string!" as Patrick describes it). SpongeBob comments on how he "should've known", but when he leaves, Patrick reveals to the audience the real secret; when he pulls the string, a secret compartment opens in the box, and there is "the embarrassing picture of SpongeBob at the Christmas party" the audience doesn't see. Patrick then tells SpongeBob "Merry Christmas".
( ‣ ) Associated production music
( • ) Original music
( ◦ ) SpongeBob music
‣Hilo March - The Hawaiian Serenaders [title card] ‣Film Fanfare (a) - Dick Stephen Walter [Patrick appears] •Vibe Sting - Nicolas Carr ["Secret box?"] •SpongeBob Closing Theme - Steve Belfer, Nicolas Carr ["Hands off, Peeping Bob."] ‣On the Beach - Kapono Beamer [SpongeBob telling Patrick all his secrets] ‣Enigma Vibe 2 - Nicolas Carr [spilled milk] ‣Chase Cue 2 - Sage Guyton, Jeremy Wakefield [SpongeBob's "secret stuff"] ‣Seaweed - Steve Belfer [Patrick looking inside his secret box] ‣ ? [drum roll] ‣Dramatic Climax - Mike Sunderland ["Nobody must know the mystery of the box!"] ‣Like Strange - Kenny Graham ["Not even... Squidward's house!"] •Steel Sting - Jeremy Wakefield [shot of Best Friends Forever ring] ‣South Pacific Island II - Victor Cavini ["I feel so filthy."] ‣Ulkereien - Gerhard Trede ["After all, this is a pretty great secret."] ‣House of Horror - W. Merrick Farran [SpongeBob worried about what's in the box] ‣Tomfoolery - David Snell ["How do you look into a secret box?"] ‣Kommissar X - Gerhard Trede [SpongeBob sneaks into Patrick's house] ‣Footsteps of Horror - W. Merrick Farran [SpongeBob trying not to make noise] ‣Danger Zone - Mike Sunderland [Patrick wakes up] ‣ ? ["It's the Best Friends Forever, Best Friends Forever ring!"] ‣Mama E - George de Fretes ["How could you do this?!"] ‣Revelation - Dick Stephen Walter [SpongeBob looks inside the box] ‣Steel Sting (a) - Jeremy Wakefield [secret string] ‣Like Strange - Kenny Graham [Patrick laughing] ‣Jingle Bells - Sage Guyton, Jeremy Wakefield [ending]
It is revealed that SpongeBob and Patrick's symbol of friendship is a ring that sings, "It's the best friends forever, best friends forever, ring!". When a button is pressed, it has dancing figures of SpongeBob and Patrick.
Running Gag: Every time SpongeBob steps on or bounces onto Patrick's house floor, it causes a loud noise.
A lot of scenes from this episode have been used on YouTube.
This is the first episode to use a real image as part of the title card instead of a drawn one. This is the same for Idiot Box.
Squidward's house was missing near the end of the episode. This also occurs in InSPONGEiac.
This episode revealed that SpongeBob and Patrick had been friends since they were babies.
The design of Old SpongeBob seen in SpongeBob's fantasy of Patrick and himself being old was used again in Goo Goo Gas.
This episode's basic plot lines bares a striking resemblance to the 'Dharma and Greg' episode "The box" which aired just eight months before.
This is one of the biggest appearances of Patrick's House.
In Polish version, this episode called Super tajne pudełko which means The Super Secret Box.
Patrick's line "Duh!" and his face is a popular internet meme.
This episode aired four days before 9/11.
Patrick says "Hands off, peeping Bob!", a reference to the phrase "peeping Tom".
When Patrick mistakes SpongeBob for the Clam-burglar, it is possibly a reference to a McDonald's character, the Hamburglar.
In the scene when SpongeBob is sneaking to Patrick's house at night, Squidward's house is missing. This error also happened in InSPONGEiac.
The potato chip on the floor that SpongeBob stepped on is in one scene, but in another scene, it is missing.
In this episode, SpongeBob is drawn as a lighter shade of yellow.
When Patrick says, "And to think we joined the 'Best Friends Forever' club?!" his purple eyelids disappear.
When SpongeBob gathers the "secret" stuff, he goes towards Patrick's House not his own.