Arguing koalas wreak havoc at the pet shop; meanwhile, Brittany ignores Whittany after she scores higher marks on a test.

Blythe takes on another job as a sales clerk and lets her spending get out of control. Meanwhile, the pets grow annoyed with a difficult doll Blythe asks them to watch.

When Blythe's enters her dress designs for the The Big, Feathered Parade at the parade's warehouse, she is promptly denied due to age restrictions. There, she comes across Ramon (voiced by Colin Murdock), the head designer of the parade, and his Common Myna, Desi (voiced by Brian Drummond). Ramon becomes impressed upon seeing her designs, and decides to steal them by switching her portfolio with his identical one. Blythe notices the replacement, and when she sees her designs being used on every aspect of the parade the next day, she sets off to reclaim ownership of them. Meanwhile, when Vinnie pairs with Zoe to quench his obsession, Bruce the iguana (also voiced by Murdock), he struggles to find a water bottle big enough for Bruce.

Roger’s super competitive sister, Mo, comes for a visit, bringing them a constant desire of outdoing each other.

The host of a reality television series informs Mrs. Twombly of buried treasure located beneath Littlest Pet Shop, belonging to one of her ancestors. Their efforts at excavation quickly become the source of irritation for Blythe when they start causing property damage, and the source of outrage for Pepper, who takes the crew's map to show to the pets. There, the roots of Littlest Pet Shop are uncovered, and the story of Henrietta Twombly is told in the form of flashbacks.

The pets suspect a Siamese cat visiting the day camp is preying on Mrs. Twombly. Meanwhile, Blythe encourages the Biskit twins to join their mathlete team after she overhears them using narratives of their daily life to solve complex math equations.

Zoe begs for Blythe to enter her in a reality television series based on a beauty pageant for dogs. What starts off as enjoyable starts to consume Blythe, who becomes driven by winning the pageant, much to the dejection of Zoe.

Blythe earns the gratitude of the Biskit twins after defending them against a bully during gym, but ends up being forced from talking her other friends. Meanwhile, Pepper is inspired to use insult comedy as part of her stand-up comedy schtick, but takes it too far on Penny while being unaware of her sensitive feelings.

Vinnie's tail falls off in an act of autotomy, and after a series of trials to find an adequate replacement for it, he is shocked to find that he becomes better at dancing without one. Meanwhile, Zoe and Pepper become rivals over the theme for a party meant for Penny Ling.

The pets are driven to madness trying to identify a hum resonating from inside the shop, while Blythe runs for class president against the Biskits.

Suspecting that he has become too serious for his own good, Russell loosens up by creating an alter ego, dubbed "Fun Russell". Meanwhile, Blythe finds her friend Sue mimicking every aspect of her personality unsettling.

Vinnie gets to tour the set of his favorite dance competition show, Shake a Leg. When his dance performance in front of the show's judges gets harshly rejected, he tearfully abandons Blythe into the streets, where he befriends an ensemble of street-dancing lizards. Meanwhile, the pets stumble around trying to find a decent spot for their remote control.

Sunil is mistaken for Shahrukh, a famous movie mongoose hailing from India. The pets bend over backwards to appease him, but quickly lose their patience at his pampered behavior during his stay at the day camp.

Russell becomes ecstatic as he reviews the plans for his first slumber party while with Blythe at the day camp. Jealous that they are not invited, Sunil and Vinnie make plans to crash their party. Meanwhile, Mrs. Twombly notices her supplies are being consumed by something, and jokingly cites a poltergeist as the cause of it, which awakens Russell's superstitions about a ghost he read up on. Later, Sunil and Vinnie's attempt by to break in to the pet shop sends the city without power, causing Russell to hallucinate an octopus-like creature trying to devour him.

Russell's excited to go to the Renaissance Faire, but then he learns corrupt activity is occurring at the event.

Sunil and Vinnie hear howling noises coming from inside the pet shop, and suspect that their friends have turned into werewolves. When Mrs. Twombly finds she has been outbid at an online auction for a highly coveted doorknob by her rival, Fisher Biskit, she takes Blythe and herself for a visit to his mansion to find its whereabouts.

An anxious moose bellows, so Blythe and the pets try to soothe it in order not to disturb Mrs. Twombly's singing quartet reunion.

A massive snow storm hits Downtown City, trapping Blythe and the pets at Littlest Pet Shop and things get tense with the pets at each other's throats. Meanwhile, Roger keeps getting lost while trying to dig through the snow to get to the pet shop to save Blythe.

Blythe stumbles to fix a botched haircut on Zoe, while the other pets urge Minka to purse the life of an art superstar, and get out of hand when they overestimate her artistic endurance.

Blythe attempts to be the peacekeeper between Zoe and her old rival Madame Pom when arrives at day camp, all the while Penny Ling and Vinnie nearly destroy the shop while practicing for their new group dance routine. Likewise, Mrs. Twombly goes on a rampage in search of her favorite cleaning spray.

Surrounded by guilt, the pets try to prove Blythe's innocence after she is accused of sending Aunt Cristie's truck careening down the street while meeting Buttercream's alley cat friend, Sugar Sprinkles.

Russell and Blythe find themselves in a (partially imagined) state of solitude.

Blythe rejects the notion of her dad going on a date to a charity ball, while Penny Ling struggles to voice her disapproval of an outfit Blythe designs for her to wear at the ball along with the rest of the pets.

Blythe enlists the pets to retrieve her new favorite necklace that fell inside a vat of batter used for filling a huge cupcake order with Youngmee. This proves difficult for them, when they discover the order was placed by Fisher Bisket for his twin daughter's "quarter-birthday" party.

Vinnie accidentally falls into a dumpster while trying to catch a fly and is transported to the dump, where he encounters a rat that helps him get back to the pet store. Blythe contracts the common cold and can no longer understand the pets, so the pets try to cure her.