Look, I even ponified the plot for you guys.
Copper Top and Hot Fuzz—identical twin sisters embarking separate paths. Hot Fuzz is an idealistic, but nonetheless respected police investigator and family mare in Manehattan, helping the local police combat the recent crime wave while working tirelessly to provide for her father, husband, and daughter. The estranged, more cynical Copper Top, in contrast, prefers the solitude of life as a security guard in the idyllic towns of Mustangia, happy to settle down after finishing her tour of duty in the Sleipnir Gray Team, one of Equestria’s elite special forces. Neither had spoken to the other for nearly two decades.
Late one night, Hot Fuzz joins a police operation investigating claims that changelings remaining loyal to the rogue Queen Chrysalis had been found in the Upper East Side. When Hot Fuzz fails to return after several days, her family grows worried. Princess Celestia personally travels to Manehatten and tells them that Hot Fuzz had been injured and must remain in hiding for a few more days lest Chrysalis’s loyalists track her down.
Several days later, Hot Fuzz indeed returns, but it is as if she is a different pony. Where there was once warm love, there is awkward unfamiliarity. Where there were memories, there is, in Hot Fuzz’s words, “bouts of forgetfulness.” Her daughter grows confused. Her husband becomes worried. And her father becomes suspiscious. All these doubts are only made worse when rumors spread within Hot Fuzz’s neighborhood that the Hot Fuzz who returned is in fact a changeling loyal to Chrysalis.
Unbeknownst to them, Hot Fuzz died weeks ago in the police operation. When word reached Princess Celestia, she formulated a plan with the benevolent, newly-appointed changeling King Thorax and ordered Copper Top to take on her twin sister’s identity and finish Hot Fuzz’s mission, placing Copper Top back in the action she tried to get away from and forcing her to face past demons. On top of tracking down the changeling loyalists who took her twin sister’s life and the corrupt police officers covering for them, Copper Top must also earn the trust of Hot Fuzz’s family while masquerading as her and amend fences with her father, a pony whom she resented since her estrangement.
At least Copper Top is not alone in her mission. There’s her fellow police officer Egres Ferguson, a farmer from Mustangia with a big heart, a big mouth, and a big tolerance for alcohol. There’s Brightmane, Hot Fuzz’s rival in the police academy. And there’s Blues Sr., director of the Criminal Investagation and Apprehension Division of the Manehattan Police Department, Copper Top’s uncle, and the only member of her family who knows of her secret.
There’s also Pinkie Pie, an eccentric tourist who crossed paths with Hot Fuzz one day while making a public disturbance, but she only goes to Manehattan once in a while to visit her favorite sister Maud.
Copper Top may be a provincial pony strengthened by her time in the Sleipnir Gray Team and the struggles of living alone in Mustangia, but it’s going to be a tough road even for her.