Kumar Mangat Pathak and Abhishek Pathak’s Guest Iin London is a cinematic version of the Hindi saying ‘Athithi Devo Bhava’. The film is about an elderly man named Gangasharan Gandothra (Paresh Rawal) and his dutiful wife Guddi (Tanvi Azmi) who come to London and land up staying in the house of Kartik (Kartik Aaryan) and Anaya (Kriti Kharbanda). Both, Kartik and Anaya are on the verge of getting married for their individual vested interests. Even though days start becoming weeks and months, Gangasharan Gandothra and his wife Guddi refrain from going back to India, thus, putting the young couple in a lot of inconvenience.
Do Gangasharan Gandothra and his wife Guddi remain forever with Kartik and Anaya in their house in London, what were the vested interests of Kartik and Anaya in getting married and what was the ultimate motive of Gangasharan Gandothra and his wife Guddi to come to London is what forms the rest of the film.