Greg Heffley and his family see an advertisement for Isle de corales, a resort where his parents went for their
honeymoon, on TV. To Greg's dismay, they skip Christmas to go to the resort instead. After multiple mishaps at the airport, such as their flight being delayed, the Heffleys board the plane. Greg is disappointed that he has to sit in the coach class seats, and is more annoyed when he is seated between a different family with a baby. After they land at the resort, Greg and his family find out that the resort has changed since his parents' honeymoon, and most of the activities they did are now on the adult-only section. In their room, they notice that they claimed the wrong suitcase and theirs was sent back home. After a visit to a crowded pool, Greg getting scared by an iguana, a meal being ruined by birds and slugs, and Frank getting diarrhea, the Heffleys go to sleep for the night. In the morning, Greg has an encounter with a tarantula that climbed into his slippers, and he loses track of where it went. He and his family go out to ride a
banana boat because Susan wants to get a Christmas card photo, but the boat gets punctured. The next day, Susan visits the spa, leaving Greg to take care of Manny. He lets Manny play at a water park, but ends up falling in water that he believes to be contaminated with urine. After this, Susan books a
snorkeling trip for the family, but Greg worries about getting stung by a
box jellyfish. He takes a gulp of water by accident and believes that he has swallowed a
sea horse, ending the snorkeling trip early. The Heffleys return to the pool, and Manny's box jellyfish, contained in a bucket, gets into the pool. During the commotion, Greg and his family sneak back into their room. The next day, Greg visits a tennis court, out of fear that the tarantula will reappear. The other kids recognize Greg as one of the people involved with the box jellyfish incident, so he is chased out of the court and runs back to his family in the hotel room. Manny knocks over the suitcase, and his family tries on the clothes inside. They go out to eat at the
golf clubhouse and play golf but are caught by security for having stolen another family's clothes and are ordered to leave the resort. The Heffleys stay at the airport hotel, and the next day, Greg's parents choose to end things on a high note and sneak back in for a family picture. After taking the picture, the family split up and run off, with Greg ending up in a
private beach on the adult side of the resort. He runs away and notices his family on the other side through a hole in the wall. The wall falls down, and a lot of people rush in, letting the Heffleys escape the resort. After he gets home, Greg visits the Isla de Corales website and finds that the resort is now appealing for information about his family's identities, and Greg says that any chance of them ever returning to the resort is gone. == Reception ==