A Little Night Music is a musical with music and lyrics by Stephen Sondheim and book by Hugh Wheeler, based on the Ingmar Bergman film Smiles of a Summer Night. The score is notable for having been written almost entirely in waltz time (3/4) or multiples thereof, and is considered one of Sondheim's greatest works (it's also one of the lightest and most accessible, Forum and Into the Woods aside, which makes it a great introduction for nascent Sondheim fans). It concerns a series of interconnected Love Triangles, which end up resolving themselves on a summer's night.The plot, set in Sweden around 1900, is centered around a rekindled romance between just-barely-fading starlet Desiree Armfeldt and newly re-married lawyer Fredrik Egerman. Fredrik is married to a much younger woman, Anne, who is the subject of his son Henrik's adoration; Desiree is having an affair with a married dragoon, Carl-Magnus, whose wife Charlotte knows Anne through her younger sister. Eventually they all end up at Desiree's mother's house in the country. Hilarity (among other things) Ensues.Not to be confused with the Pokémon fanfic or the Mozart composition.
Betty and Veronica - Desiree as Archie, Fredrik as Betty, Carl-Magnus as Veronica. Alternatively, Fredrik as Archie, Desiree as Veronica, Anne as Betty. The Henrik/Anne/Petra triangle kinda fits this as well.
Billing Displacement - On a fairly regular basis, including both Broadway productions, the actress playing Madame Armfeldt gets top billing alongside the leads (Desiree and Fredrik), despite not having nearly as large a part. In particular, the recent revival gave Angela Lansbury higher billing than Alexander Hanson, who played Fredrik, because... well, because she's Angela Lansbury.
"Silly People," sung by Frid, cut because nobody knew nor cared who Frid was
Deadpan Snarker - Charlotte, Mme. Armfeldt, Desiree (especially in "You Must Meet My Wife")
Demoted to Extra - Frid played an important part in Smiles of a Summer Night, but his role in the musical was essentially reduced to one scene (even his song was cut).
Elopement: Anne and Henrik elope near the end of the play. Since Anne is already married to Henrik's father this is really the only option.
Endless Daytime: Act II has a thematically appropriate but otherwise Irrelevant Act Opener by the chorus called "The Sun Won't Set", in which it stays twilight till around 11pm (because Act II takes place near the Arctic Circle during summer).
Epic Rocking - "A Weekend In The Country," only upbeat and hilarious.
Life Imitates Art - Victoria Mallory and Len Cariou, the actors for Anne and Frederik, were dating when the original production opened. When it closed, Victoria Mallory ran away with Mark Lambert, Henrik's actor. Their daughter, Ramona Mallory, played Anne in the 2009 Broadway revival. note It is perhaps worth noting that though their characters were 18 and 40something, respectively, Mallory and Cariou were themselves 24 and 34 during the run, not nearly so unusual an age gap.
Love Dodecahedron - Except it's not a complicated jumble so much as an extensive line: Charlotte <-> Carl-Magnus <-> Desiree <-> Fredrik <-> Anne <-> Henrik <-> Petra <-> Frid
This line is also a series of interlocking Love Triangles, with Carl-Magnus, Desiree, Fredrik, Anne, Henrik and Petra each forming the apex of a Type 7 love triangle, in which those either side of them on the line are the other corners. Charlotte also attempts to make Fredrik the third corner of a love triangle with Carl-Magnus and herself at one point, unsuccessfully.
May-December Romance - However, Anne and Fredrik don't end up together, and this is portrayed as a good thing.
Mythology Gag - In Smiles of a Summer Night, Fredrik falls into some water at Desiree's house, soaking his clothes, and so Desiree gives him Carl-Magnus's robe to wear while he waits for them to dry; Carl-Magnus arrives and is outraged, suspecting shenanigans. In A Little Night Music, the innocent explanation is dispensed with: Fredrik and Desiree actually do have sex. But when Carl-Magnus arrives, they tell him that Fredrik fell in the water, and so Desiree gave him Carl-Magnus's robe to wear while he waits for his clothes to dry...
Not What It Looks Like - Anne and Fredrik walk in on Petra... fixing Henrik's pants. Although no one actually says the magic words, and while it's not sexual itself, it does happen right after Henrik and Petra's attempt at sex (see The Loins Sleep Tonight above).
Rule of Three - The whole work is structured around threes and triangles. The music is mostly in waltz time (3/4) or variations thereof. The cast is, apart from Madame Armfeldt and Fredrika, structured into a series of interlocking love triangles (see Love Dodecahedron above). There are songs sung by three people ("Now/Later/Soon"), and songs sung by two people about a third person ("You Must Meet My Wife" and "It Would Have Been Wonderful" most prominently). The summer night smiles three times.
In original orchestrator Jonathan Tunick's foreword in the published script of the show, he takes this a step further, saying how the show is about the unstable three progressing into the stable two—by the end all of the love triangles are resolved.
The original idea for the show was to go through the story three times - once as a tragedy (which would've ended with Fredrik committing suicide), once as a farce, and one final time where everything goes properly.