One drizzly and dark day in Bournemouth, England, the Durrells sit in their living room, fighting their usual ailments brought on by the weather. Larry, the eldest son, is irritated and suggests that they escape the weather by moving to Corfu, Greece. Though Mother says the idea is ridiculous, she agrees. The family packs their most precious belongings—Gerry brings his scientific equipment and the family dog, Roger; Margo brings her acne potions; Leslie brings his guns; and Larry brings books—and they arrive in Greece not long after. The family is a sight to behold during the cab ride to the hotel, as Roger barks viciously at strays on the street and tries to jump out. Mother and Margo are immediately disgusted and worried about disease when they discover that there are funerals galore that day and that Grecian bathroom practices are less sanitary than English ones, so Mother sets out to find a villa immediately. Her first guide, Mr. Beeler, isn't helpful, as he doesn't understand why she wants a bathroom in the house. On the second day the family meets Spiro, a Greek man who speaks English. He shows them what becomes their new home, a pink villa on a hill.
Gerry and Roger spend their time in the garden, where Gerry closely observes the bugs in the flowers. He soon learns Greek and makes friends with the locals. The shepherd Yani tells Gerry folktales about cypress trees, and the peculiar Rose-Beetle Man sells Gerry several pets. Gerry acquires the tortoise Achilles first, who is warmly accepted into the family. He dies not long after when he falls into a well. Gerry purchases a dove named Quasimodo next. Though Quasimodo is a fun pet for a time, Gerry soon discovers that Quasimodo is actually female. She becomes very wild after she lays eggs.
Mother soon decides that it's time for Gerry to be educated. Larry suggests that his friend George tutor Gerry. George is a fine tutor according to Gerry; he sprinkles in zoological "facts" of questionable truth and, most importantly, teaches Gerry how to properly observe animals and record his findings. One afternoon, Gerry goes out with Roger to explore and swim. They stop and see Yani and on their way back home, Gerry discovers strange nests. He seeks out George to explain the nests and discovers that George is visiting with the esteemed scientist, Dr. Theodore Stephanides. Theodore treats Gerry like he is a knowledgeable adult and explains that the nests belong to trapdoor spiders. Several days later, Theodore sends a gift of a pocket microscope to Gerry and invites him for tea. Gerry begins spending every Thursday afternoon at Theodore's house, poring over microscope slides and consulting books.
When spring arrives, Mother's cooking causes Larry to develop indigestion, and Margo begins secretly swimming with a Turk. Spiro is distraught. When Margo introduces the Turk to the family, they find him condescending and smug. Mother insists on accompanying Margo and the Turk to the cinema the next night, after which the relationship ends due to the Turk's horribly strong perfume. As summer approaches, Larry writes to a number of friends inviting them to stay. Mother insists that they cannot host anyone given the small size of their villa, but Larry believes the obvious solution is to move to a bigger one. Despite Mother's protests, the family does just that. The new villa is yellow and is surrounded by many trees. Mother hires a woman named Lugaretzia to help with the house, though Lugaretzia turns out to be difficult to work with and a hypochondriac. The furniture in the yellow villa is in bad shape, so Mother asks Spiro to take her, Gerry, and Margo into town to buy new pieces. In town, they get swept up in a procession heading for the church to kiss the feet of Saint Spiridion, the patron saint of the island. Despite Mother's attempts to tell Margo not to, Margo kisses the saint's feet and comes down with the flu immediately. Gerry occupies his time watching swallows build nests in the eaves of the house.
With summer comes the tortoises. Gerry watches their mating rituals on the hill behind the villa and even collects an egg from his favorite tortoise, Madame Cyclops. Larry's friends arrive in waves. The poet Zatopec arrives first, followed by the three young artists Jonquil, Durant, and Michael. Though they all want to work, none of them make any art during their stay. Larry also invites a countess named Melanie, who suffers from a skin infection. Mother mistakenly believes that Melanie has a venereal disease and calls Theodore to assess the situation, and she's mortified to discover her mistake. At dinner that night, Theodore tells the table about a theatre production gone wrong. When Larry insists that such a thing couldn't have happened, Theodore explains that anything can happen in Corfu.
Gerry greatly enjoys watching scorpions in the wall behind the house. One day, he finds a mother scorpion covered in babies, captures her in a matchbox, and brings her inside. Poor Larry opens the matchbox when he tries to light a cigarette and pandemonium ensues. After this, Mother decides that Gerry needs to resume his education, so she sends him to the Belgian consul to learn French. Gerry doesn't learn much, but the Belgian consul spends a fair amount of time shooting sickly stray cats out his window, which teaches Gerry that death can be humane when an animal is suffering.
Theodore comes on Thursdays so he can watch the weekly seaplane land from the Durrells' attic, and he teaches Gerry a great deal about science and aquatic life. The following summer, Mother hires Peter to tutor Gerry. Gerry also receives his own room in the house to keep his specimens and animals. One afternoon, Gerry discovers a baby owl in a tree and brings it home. The family names him Ulysses. Though he is initially extremely aggressive, he soon mellows and even decides that Roger is a fine companion. The Durrell children and Peter begin swimming at night to escape the heat, and Gerry is thrilled when porpoises visit. Eventually, Mother purchases a horrendous and outdated swimming costume so she can join, and the family plans a moonlit picnic for her first swim. Theodore joins and they all watch a magnificent show as the fireflies dance and the porpoises swim in the phosphorescence.
Gerry discovers a small archipelago after the family invests in an outboard engine for their boat the Sea Cow, though they forbid him from taking it out himself. Gerry asks Leslie to build him a boat for his birthday. Two weeks later, Leslie unveils the boat. It's round and strange, but Gerry loves it. He names it the Bootle-Bumtrinket. Its launch is eventful when Peter gets dumped into the water. The party that night is amazing, and Gerry receives two puppies that Larry names Widdle and Puke. Not long after, the family decides that Margo and Peter have become too fond of each other, so Mother fires Peter. Margo cries and pouts dramatically for weeks. Leslie rigs up a complicated system of guns when he notices items missing from the Sea Cow but doesn't share this with the family. When he shoots at the thieves, Mother fears Margo committed suicide. Though this event causes Margo to stop pouting, she does take the Bootle-Bumtrinket out to a small island to pout in peace and receives a very painful sunburn on her eyelids.
As winter comes, Leslie begins hunting boar on the mainland. Larry maddeningly insists that hunting is easy, even after Leslie performs an especially difficult maneuver. Leslie invites Larry to come out to show everyone how it's done. Larry not only misses the birds, but falls into the deep mud and can barely get out. Angry, he takes three bottles of brandy to bed, drinks two, and falls asleep. A coal falls out of his fireplace and sets a supporting beam on fire, which sends the family into a tizzy when they discover it. Larry, unconcerned, instructs his family on how to put it out from bed. When spring arrives again, Mother receives a letter from Great-Aunt Hermione asking to visit. Nobody likes Hermione, so Larry insists they need to move to a smaller house so she can't come.
The next villa is white and is also the home of massive praying mantises and geckos. A gecko Gerry calls Geronimo hunts in his room every night and is very aggressive. One afternoon, Gerry catches a female mantis he believes is going to lay eggs. He names her Cicely and she soon escapes. That night, she resurfaces and she and Geronimo fight to the death, with Geronimo emerging victorious. Gerry also finds two toads that are so big, one eats a gecko. Mother soon hires a man named Kralefsky to tutor Gerry, insisting that he's a bird lover. Gerry is skeptical but at his first lesson, he finds that Mother was right: Kralefsky is an aviculturist and breeds birds. Despite this wonderful hobby, Kralefsky is a difficult tutor. He also strangely visits his mother often, which Gerry believes is Kralefsky's way of talking about the bathroom. After several weeks, Gerry discovers that Kralefsky does actually care for his mother in the house. Mrs. Kralefsky tells Gerry that her advanced age means that she can hear flowers speak.
One afternoon, Gerry takes two magpie babies out of a nest and brings them home. The birds are soon christened the Magenpies. Though Larry is initially afraid they'll steal, he forgets about their criminal tendencies until one day they raid his room and destroy his manuscript. He insists that Gerry lock them up, so Gerry asks Kralefsky to help him build a cage and at the same time, teach him to wrestle. Gerry believes that Kralefsky can wrestle because in comparison to Kralefsky's other stories, his one about wrestling seems plausible. However, Gerry seriously injures Kralefsky when Kralefsky tries to teach him some "tricks." Not long after, Mother brings home a female dog named Dodo. Dodo proves difficult, as she goes into season regularly and won't let Mother out of her sight. She has one puppy with Puke. During an excursion to a beautiful lake, Theodore regales them with a tale of an opera performance that went very wrong. Several weeks later, Gerry attempts to capture a terrapin named Old Plop and instead, captures two water snakes. He also meets a convict named Kosti, who gives Gerry a cantankerous gull named Alecko. Larry fears that Alecko is an albatross, while Mother is more concerned that Gerry is spending time with murderers.
In September, the Durrells throw a Christmas party. Things go wrong from the start: the now-captive Old Plop and the snakes eat Gerry's goldfish; the snakes get heatstroke and need to cool down in the bathtub; and the Magenpies and Alecko escape and wreak havoc. Leslie is terrified to discover the snakes in the bathtub, though the guests wonder if he's sane. Dodo is in season and a dogfight erupts in the middle of cocktail hour, and Larry regales everyone with tales of how dangerous the house is. Soon after, Kralefsky insists he has nothing more to teach Gerry, so the Durrells prepare to return to England so Gerry can finish his education. As they pass through Switzerland, Mother is incensed when an immigration official writes that the Durrells are a "traveling circus and staff."