The title refers to the black-and-white aesthetic of the episode. Chiaroscuro is an artistic technique that uses strong lights and darks (chiaro, bright and oscuro, dark) to create contrasts, so as to give a starker, more dramatic and sometimes three-dimensional feel to the two-dimensional image. A notable user was Leonardo Da Vinci, whose hologram has made a number of appearances in Star Trek (VOY: “Scorpion, Part 1”).

The stardate is 2122.4. The system shown on screen is Mat’Aar, its first appearance in lore. The technobabble explanation for the black-and-white look is the “infrared blackbody spectra” from the Mat’Aaran star whose radiation affects how people see colour. This is the same explanation as to why the outdoor scenes on the Harkonnen homeworld of Gledi Prime were black-and-white in the movie Dune: Part Two.

The last time the Klingons and the Federation were in open conflict was during the Klingon War of 2257-2258, some 5-6 years ago from SNW’s present day. Since then, the two powers have enjoyed an uneasy peace, which will once again erupt into open conflict a few years from now in 2266-67 (TOS: “Errand of Mercy”).

With Una on the mission is Uhura and M’Benga. The latter served in the Klingon War as a special forces operative code-named “The Ghost” (SNW: “Under the Cloak of War”).

Una’s fondness for rules is why the crew nicknamed her “Where Fun Goes to Die” (SNW: “Spock Amok”).

The art deco architecture and fashion of Mat’Aar XII, coupled with the black-and-white motif and plot are designed to evoke a 1940s film noir atmosphere, with the Klingon occupation, resistance and collaborators reminiscent of other films of the era like 1942’s Casablanca.

M’Benga’s reference to Una pretending to be someone she’s not refers to her years hiding her Illyrian heritage (SNW: “Ad Astra Per Aspera”).

Uhura quotes partially from Casablanca, “Of all the gin-joints in all the towns in all the world… she walks into mine.”

La’An’s transformation into a Vulcan took place in SNW: “Four and a Half Vulcans”, where she began to exhibit aggressive and paranoid traits more commonly associated with Romulan culture. Some of it was chalked up to her Augment heritage.

The legendary Commander Kor was first played by the inimitable John Colicos in “Errand of Mercy”, who subsequently reprised the role in DS9: “Blood Oath”, “The Sword of Kahless” and “Once More Unto the Breach”. As M’Benga notes, Kor is a member of the House of Kor, part of the Klingon Imperial Family (“Once More Unto the Breach”), which traces its descent from Kahless the Unforgettable, founder of Klingon civilization (TOS: “The Savage Curtain”). He is played here by actor Demore Barnes who, like Colicos, is Canadian.

The machine the resistance woman refers to is the Klingon mind scanner (“Errand of Mercy”), also known as a mind sifter or mind ripper, which scans a subject’s thoughts but sometimes destructively. M’Benga alludes to the idea that in a vast universe, we will eventually run into our own doppelgängers. This is the kind of excuse that TOS came up with to explain the number of Earth-like civilizations Enteprise ran into by citing “Hodgkin’s Law of Parallel Planetary Development” (TOS: “Bread and Circuses”).

M’Benga refers to the Borgia plant, which is similar to the nightshade plant and common to Class M plants (TOS: “The Man Trap”). The Borgias were a powerful Renaissance family that were reputed to use poison to eliminate their rivals.

Kor is shown as a ridge-headed Klingon, unlike his depiction in TOS but in line with how he is portrayed in DS9. The whole Klingon ridges thing is a rabbit hole I really don’t have space to get into right now, but I’m sure someone will bring it up elsewhere in a thread.

Kor’s claim that serving the Empire is the noblest honour reminds me of the concept of kuve, or “servitor” species in the seminal TOS novel The Final Reflection which, although rendered non-canon by events, heavily influenced the depiction of Klingons as a sophisticated warrior culture. In the novel, the Klingons’ position is also that there is no shame in being conquered and rendered kuve because they are serving a superior species.

Uhura uses the alias Nyota Nakuru. M’Benga was born in Nakuru, Kenya on 29 December 2223 (“Under the Cloak of War”). Neodymium is a real-world rare earth element, commonly used in magnets, but it is mentioned in DS9: “In the Cards” as being part of a neodymium power cell. Here Kor mentions it in conjunction with munitions.

Allakas malt was an alcoholic beverage first mentioned in ENT: “The Communicator”.

A targ is a Klingon animal, like a cross between a pig and a dog, and often domesticated.

Scotty says, “Cross my heart, hope to get stuck in a pattern buffer.” He will, in fact, be stuck in a transporter pattern buffer for 75 years (TNG: “Relics”), but on purpose.

M’Benga says that a parent would do anything to protect their child. He might be thinking about his own daughter, Rukiya, for whom he took extraordinary measures to preserve her life when she was dying from chinokemia (SNW: “The Elysian Kingdom”).

This is the first time the T’Gal regional dialect of Klingon has been mentioned.

The Klingons entering the club are singing the same drinking song Worf and Huraga sang in DS9: “The Way of the Warrior”. The Doctor and Seven also sing it in VOY: “Barge of the Dead”. The Mat’Aarians singing back in defiance copies an identical scene from Casablanca where German soldiers singing the patriotic “Die Wacht am Rhein” are drowned out by other patrons singing the French national anthem “La Marseillaise”.

Bloodwine is a Klingon alcoholic beverage which is made from stomping on serpent worms in the same way wine is made from grapes on Earth (LD: “A Farewell to Farms”).

The USS Yang (NCC-321616) was a 32nd century Friendship-class starship (DIS: “That Hope is You, Part 2”, SFA: “Rubincon”). Chapel’s Yang would be, of course, the 23rd century namesake.

This is the first mention of Ülget in lore.

As the shuttle leaves the system, colour fades back into the closing scene.