Act I

The show opens on a bare stage, save for an odd red-and-white-striped hat in the center. A small boy wanders into view and notices the hat, wondering to whom it might belong. He finally mentions the word Cat in the Hat, who appears before the Boy and tells him he has been brought to life by the Boy's "Thinks". The Cat urges this boy to Think up the "Seussian" world and characters around the boy and himself ("Oh, the Thinks You Can Think!"). The Cat then reveals to the Boy that he is about to tell a story about someone as imaginative as the Boy is.

To begin the story, the Cat encourages the Boy to think up the Jungle of Nool, where Horton the Elephant is bathing. Horton hears a strange noise coming from a nearby speck of dust, and reasons that someone must be on it, calling out for help. He carefully places the speck on a soft clover and decides to guard it ("Horton Hears a Who"). But he is mocked mercilessly by the Sour Kangaroo and the other animals of the jungle, who do not believe him ("Biggest Blame Fool"). The only exceptions are Horton's bird neighbors, Gertrude McFuzz, who admires his compassion, and Mayzie LaBird, who is more concerned about herself.

Horton soon discovers that the speck is actually a microscopic planet populated by creatures called Whos. The citizens of Who-ville introduce themselves and their yearly Christmas pageant directed by their friend the Grinch. They also reveal that in addition to being unable to control where the speck flies, they are on the brink of war and their entire population of Truffula Trees has been cut down ("Here on Who"). The Whos thank Horton and ask for his protection, and he agrees to guard their planet.

At this point, the Cat pushes the Boy into the story; he becomes Jojo, the son of the Mayor of Who-ville and his wife. Jojo has been getting into trouble at school for having Thinks, so his parents order him to "take a bath and go to bed, and think some normal Thinks, instead".^[2] Jojo blames the Cat for getting him into trouble and tries to send him away. The Cat refuses and persuades Jojo to imagine the tub is McElligot's Pool ("It's Possible"). Jojo inadvertently floods the house, leading the Mayor and his wife to contemplate what to do with their son ("How to Raise a Child"). When the Cat hands them a brochure, they decide to send Jojo to a military school run by General Genghis Khan Schmitz, who is preparing to go to war with those who eat their bread with the butter side down ("The Military"). While there, Jojo meets Horton, and finds a mutual friend in him ("Alone in the Universe").

Gertrude, meanwhile, has fallen in love with Horton, but is afraid he does not notice her because of her own tail, which consists of only "one droopy-droop feather" ("The One Feather Tail of Miss Gertrude McFuzz"). At the advice of Mayzie, whose tail is enormous and dazzling, she consumes pills which make her tail grow new feathers. Gertrude is so excited that she overdoses, causing her tail to grow long and unwieldy ("Amayzing Mayzie"/"Amazing Gertrude").

Horton is ambushed by the Wickersham brothers, a gang of delinquent monkeys, who steal the clover and make off with it ("Monkey Around"). Horton gives chase until the Wickershams hand the clover to an eagle named Vlad Vladikoff, who drops it into a large patch of identical clovers ("Chasing the Whos"). Here, the Cat cuts briefly into the action to remind the audience how lucky they are to not be Horton ("How Lucky You Are"). Undeterred, Horton begins to look for the clover, hoping the Whos are still alive, when Gertrude catches up with him and tries to get him to notice her new tail. Horton is too busy, so she leaves to take more pills ("Notice Me, Horton").

Horton is about to search his three millionth clover when he loses hope. Mayzie, sitting in a nearby tree, offers to help him forget about the Whos by hatching an egg that she is too lazy to care for ("How Lucky You Are (Reprise)"). Horton reluctantly agrees, and Mayzie leaves for a vacation. Horton sits through months of harsh weather as he tries to decide between the egg and the Whos ("Horton Sits on the Egg") before he is captured by hunters, who take him away along with the entire tree. Gertrude tries to stop the hunters, but cannot fly due to her heavy tail.

The Cat closes the act with a reprise of "How Lucky You Are", and conducts the band during the intermission.

Act II

Horton, still hatching the egg, is auctioned off to the traveling Circus McGurkus ("Egg, Nest, and Tree"/"Circus McGurkus"/"How Lucky You Are (Reprise)"). At one show in Palm Beach, he meets up with Mayzie, who insists that he keep the egg for himself before leaving ("Amayzing Horton"). Horton mourns the loss of the Whos and Jojo, but vows just as surely to protect the egg, as it, too, is alone without its mother ("Alone in the Universe (Reprise)"), and sings it a lullaby with Jojo about a magical place called Solla Sollew. At the same time, the Mayor and his wife begin to miss Horton and Jojo, and wish for Solla Sollew, as well ("Solla Sollew").

Jojo is with General Schmitz and his platoon as the Butter Battle commences. Jojo deserts Schmitz, but sprints into a minefield and vanishes in an explosion. Schmitz assumes the worst and heads to Who-ville to tell Jojo's parents that their son has died. The Cat returns to perform a re-enactment of the dramatic scene. But in reality, Jojo has survived, but is lost with no idea of where to turn. The Cat appears to him with a band of Hunches, encouraging him to use his Thinks to find his way home ("Havin' a Hunch"). Jojo does so and happily reunites with his parents, who forgive him for his Thinks.

Gertrude sneaks into the circus to free Horton, explaining she plucked out all but one of her tail feathers to fly there, and confesses her love for him. She also reveals she has found his clover, delighting and relieving Horton to find the Whos alive and well ("All For You"). However, the Sour Kangaroo and the Wickersham brothers arrive to take Horton back to the jungle.

In the jungle, Horton is put on trial for the crimes of "talking to a speck, disturbing the peace, and loitering... on an egg" ^[2] ("The People Versus Horton the Elephant"). Aided by Gertrude, Horton makes his best case, but Judge Yertle the Turtle finds him guilty. He orders Horton remanded to the "Nool Asylum for the Criminally Insane" and the clover destroyed in a kettle of hot "Beezle-Nut" oil.^[2] Desperate, Horton encourages the Whos to make as much noise as possible to prove their existence, but the animals do not hear them. Jojo finally uses his Thinks to conjure a new word, "Yopp", which he shouts loudly enough to reach the animals' ears. Convinced at last, the animals repent and promise to help protect the Whos, and Horton is acquitted. Jojo is accepted by his parents and the rest of Who-ville as "Thinker Non-Stop" for saving their planet. Horton's egg hatches into a tiny flying "Elephant-Bird", amazing everyone, but dismaying Horton, who panics at the thought of flying progeny. Gertrude reassures him that they can raise the child together, and they agree to do so.

With the story finished, the Cat returns to close the show ("Finale - Oh, the Thinks You Can Think!"), then vanishes along with the scenery, leaving only his hat and Jojo, who is now the Boy again. The Boy picks the hat up, dons it, and says, "Seuss!"

During a curtain call, the company performs a number based on Green Eggs and Ham ("Green Eggs and Ham").

Notable Broadway replacements

• The Cat in the Hat: Rosie O'Donnell, Cathy Rigby
• Jojo: Aaron Carter, Cameron Bowen, Andrew Keenan-Bolger

Major characters

• The Cat in the Hat, the narrator of the story, the Cat also appears as the following minor characters:
  • Doctor Dake - during "Amazing Gertrude" and "All for You"
  • Louie Armstrong / Piano Player
  • Auctioneer
  • Mr. McGurkus, the owner of the Circus McGurkus
  • Jose the Pool Boy - during "How Lucky You Are" (Reprise)
• Jojo, an imaginative and misunderstood young boy
• Horton, a compassionate and determined elephant
• Gertrude McFuzz, a shy bird who falls in love with Horton and endeavors to help him
• Mayzie La Bird, Horton's vivacious, lazy, self-centered, generous, and fun-loving bird neighbor

Minor characters

• Sour Kangaroo, the boisterous rude voice of the jungle who turns everyone against Horton
• Bird Girls, Mayzie's friends, who act as a Greek chorus
• Wickersham Brothers, a gang of monkeys who mock Horton and steal the clover
• Mr. Mayor, the newly elected mayor of Who-ville and Jojo's father
• Mrs. Mayor, the Mayor's wife and Jojo's mother
• General Schmitz, the warmongering leader of the butter battle
• The Grinch, a notable resident of Who-ville who is responsible for organizing the Christmas pageant based on the tale of his own redemption
• Young Kangaroo, the child of Sour Kangaroo
• Yertle the Turtle, the judge who presides over the Jungle of Nool's court
• Vlad Vladikoff, an eagle who helps the Wickershams lose the clover

Other characters

• Whos - citizens of Who-ville
• Cadets - members of Schmitz's platoon
• Jungle Creatures - chorus and dancers in jungle scenes
• Hunches - dancers in "Havin' a Hunch"
• Circus Animals - the animals of the Circus McGurkus

• Fish - residents of McElligot's Pool during "It's Possible"
• Thing 1 and Thing 2 - help the Cat work Jojo's imagination in "A Day for the Cat in the Hat"

Pre-Broadway

In a reading in New York City, Eric Idle played the Cat in the Hat, and was credited at the time for contributions to the story line. In the Toronto workshop in 2000, coordinated by Livent Inc., Andrea Martin played the Cat in the Hat.^[3] Positive early buzz set off a bidding war among New York theatre producers, with Barry and Fran Weissler acquiring the rights.^[4] The musical had its out-of-town tryout in Boston, Massachusetts at the Colonial Theatre in September 2000.^[5]

An extensive sequence adapting The Lorax was seen in the original script, which involved Jojo meeting the Once-ler after deserting the army, and receiving the last Truffula Tree seed from him, giving him the courage to save Who-ville. Relevant characters included the Lorax himself as well as Bar-ba-loots, Swomee-Swans, and Humming-Fish, who would all appear and disappear as the Once-ler told his story. The sequence faced numerous difficulties due to the show's already lengthy running time, and was ultimately cut entirely after its Boston tryout.

Broadway

Seussical opened on Broadway at the Richard Rodgers Theatre on November 30, 2000.^[6] It was directed by Frank Galati and choreographed by Kathleen Marshall. Marshall's brother Rob Marshall was hired to direct the show when it returned to Broadway from Boston, though was uncredited. Originally, Catherine Zuber was the costume designer who made costumes as close to Seuss's illustrations as possible, and her costumes were seen in the Boston run. However, for Broadway, Zuber was replaced by William Ivey Long, whose costumes were more realistic and clashed with the Seussian set design.^[7] David Shiner played the Cat in the Hat, while Kevin Chamberlin played Horton, Michele Pawk played Mayzie LaBird, Stuart Zagnit and Alice Playten played Mr. and Mrs. Mayor, and Sharon Wilkins played the Sour Kangaroo.

The show received almost universally negative reviews.^[4] In January 2001,^[6] in response to falling ticket sales, producers brought in Rosie O'Donnell to replace Shiner as the Cat in the Hat for a month-long engagement. O’ Donell also came in because Shiner went on vacation to see his wife in Germany. The move was criticized as stunt casting, but was successful at temporarily boosting ticket sales. After O’Donell’s run ended, Shiner returned to Seussical as the Cat in the Hat in February until March. ^[4] In March, young pop star Aaron Carter and former Olympic gymnast Cathy Rigby were cast as JoJo and the Cat respectively for short engagements. Due to poor box office, the show closed on May 20 the same year after 198 performances.^[6] Its ultimate financial losses were estimated at $11 million, making it one of the worst financial flops in Broadway history.^[4]

US tours

Following the Broadway production, there were two US national tours. Rigby reprised her role as the Cat for the first tour which ran from September 2002 to June 2003.^[8][9] A second non-Equity production toured from 2003 to 2004.^[10]

The script for the first tour was reworked extensively after the show's poor showing on Broadway, resulting in the removal or reworking of several songs. The biggest change involved Jojo, who would now initially appear as an anonymous boy imagining the events onstage before the Cat pushed him into the story. Additional dialogue was included, and some songs and their reprises were cut. This version of the show is the one currently licensed by MTI as Seussical the Musical.

Off-Broadway

A 90-minute Off-Broadway production was staged at the Lucille Lortel Theatre in 2007 by Theatreworks USA. It was directed and choreographed by Marcia Milgrom Dodge.^[11][12] This production was downscaled for the National Tour, which had its last show in spring 2018.

West End (London)

Seussical opened on the West End at the Arts Theatre on December 4, 2012, presented by Selladoor Worldwide.^[13] It returned in 2013.^[14]

Off West End (London)

Seussical opened at the Southwark Playhouse on 22 November 2018, and ran for only 7 performances.

South Africa

Seussical opened at the Lyric Theatre at Gold Reef City on December 20, 2019 for the festive season, presented by &CO.

Original Broadway production

Original Off-Broadway production