Restaurant at the end of the Universe is a book written by Douglas Adams, which is a sequel to The Hitchhiker's Guide to the Galaxy. It is a science fiction comedy that takes the reader on a journey beyond the boundaries of the universe, exploring the unknown and bizarre.

The story starts with the characters from the first book, Arthur Dent, Ford Prefect, Zaphod Beeblebrox, Trillian, and Marvin the Paranoid Android, who are still on their quest to find the answer to the ultimate question of life. They are aboard the stolen spaceship Heart of Gold, where they have been traveling for a while. Along the way, they decide to stop at the Restaurant at the End of the Universe, which is located in a time warp in the future.

The Restaurant at the End of the Universe is a popular hangout spot for the wealthy and curious from all over the universe. To each table, the guests are given a copy of the menu that features dishes from different planets and dimensions. The whole restaurant is designed to cater to the guests' desires, and the menu is tailored to their tastes.

During their meal, the group is introduced to Hotblack Desiato, a rock star who has recently died in a freak accident. Hotblack's estate has hired a group of creatures called the Disaster Area crew to play a final concert in his memory, which will take place in the heart of a massive artificial black hole. The crew's ship will generate the energy required for the performance, and the ship's engines will be ignited just before the show, causing a giant explosion that will destroy the whole planet.

While the crew is watching the show, Arthur Dent discovers a new plan to find the ultimate question to life. The plan involves him going back in time and discovering the question that prompts the answer "42" – a reference to the first book in the series, where it is revealed that the answer to the ultimate question is 42. To do this, he enlists the help of a group of beings known as the Grebulons, who are notorious for their love of cricket, and who have traveled to the end of the universe to witness the final cricket match, where they will be asked the ultimate question.

However, as the group tries to leave the restaurant in their stolen spaceship, they are intercepted by a group of robots called the Golgafrinchams. The Golgafrinchams are responsible for deceiving their own civilization into thinking that they are a lower form of intelligence, therefore allowing them to be sent to another planet to continue their existence away from their home planet. However, they have now become stranded in the past and are looking for a way out. In their desperation, they decide to steal the Heart of Gold and take the rest of the group with them.

The group is taken to a new planet where the Golgafrinchams attempt to set up a new civilization with the help of the advanced technology they have stolen. While there, Arthur meets Fenchurch, a woman who has been struck by the same phenomenon that caused every living being on Earth to be teleported away before its destruction.

Eventually, the group succeeds in rescuing the Heart of Gold, but are still pursued by the Golgafrincham ship. They make it back to the Restaurant at the End of the Universe, where they are able to escape from the Golgafrinchams and the Heart of Gold is destroyed in the process. The group is then able to continue on their journey, with Trillian remaining on the planet where they had made their stop over.

The book ends with a final message from Douglas Adams about the universe, and how it is important to have fun, even in the face of danger and uncertainty.

Overall, Restaurant at the End of the Universe is a hilarious and thought-provoking book that explores concepts of time travel and the potential dangers of advanced technology. The vivid characters and bizarre situations make for an entertaining read, and the book raises questions about the nature of existence and the purpose of life.