Takes place in an earth-pony/pegasus/unicorn inhabited kingdom called Clamshell, near the seaponies and allied with Equestria.
Ruled by King Scepter the Kindly, and the next-in-line is Prince Tuna the Fluffy. Prince Shot the Fearsome is a griffin prince passed over for emperor by his other three brothers, and had been sent to live in the Clamshell Castle to learn pony etiquette in preparation for his future role as the Griffin Empire-Clamshell ambassador. Shark Slash (swordspony of seapony/earth pony heritage, aggressively chaotic and strong, combining the best traits of his ancestors) is the Head of Prince Shot's guards, which consist of Prism Sunshine (a rainbow-striped zebra healer and martial artist), Parabola (another griffin, but a devoted servant of Prince Shot who came along), and the rest of the ponified Varia Guardians, basically.
In which Foggy Fan is a cousin of the Pie family, can be easily mistaken as the equally-expressionless twin of Maud Pie, is nevertheless a pale peach pegasus with a teal mane and a teal cutie-mark of wispy clouds (a.k.a. fog), whose special talent is extraordinarily efficient fog-making or fog-dispelling weather magic. He insists on calling it 'Mist skills', and calling himself a 'top magician,' which seems to amuse himself to no end, and is the apprentice of the famous unicorn Pineapple Dream (who has an adopted sister-unicorn called Chrome Coaxer, dealing in the subtler, delicate magical suggestions).
Pineapple studies Fog's strong weather magic, basing many of his legendary illusions on the magic of the pegasi, and attempts to find a way for pegasuskind and unicornkind to mesh their magic together. His latest breakthrough is successfully teaching Fog to create illusions amidst his mist. Kenny "Ken" Fang is Chrome's pet dog. Poison "Chika" Needle is Pineapple's earth pony lab assistant and the unofficial official caretaker of Ken.
The story starts with Pineapple informing Fog that he's been requested at the Castle to solve the sleeping problems of Prince Shot, since Pineapple is too busy with a near-breakthrough, Chrome is too nervous to go to the Castle, Chika is needed at the labs, and Pineapple has taught Fog how to lace a conjured mist with sleep magic and send it through the person, thus enabling the caster to Dreamwalk the sleeper and find the root of the problem.
Also, Pineapple wants to get rid of Fog, since he's annoying, and thus detrimental to the sort of environment Pineapple needs to achieve that breakthrough.
Fog accepts (not like there's a choice), and duly sets off, meeting much of the ponyfied KHR crew on his way to the Castle (which is really only about ten miles away, but the Castle Treasurer [Mammoth Viper] is too cheap to provide a carriage/or guide/or map, and Pineapple basically just pushed him out the door with a letter of validation without room to protest).
Then he arrives at the Castle, to the chaotic scene of Bell Crown attempting to gain alicorn status and thus become a real Prince. Somehow, this involves Bell trying to murder ("grievously injure!" he protested) his twin brother Razz Eel and his pet elephant Olgbert, who are ambassadors from the High Noble Orchid Chalk's Grand Estate.
It gets worse from there.