Existentialism can be understood as the belief that the world lacks inherent meaning and that individuals can carve out meaning for themselves through their experience. In Custody clearly shows existentialist themes through the disillusionment that Deven goes through upon meeting his hero, Nur Shahjehanabadi.
Whereas a more pessimistic perspective might lead to Deven tuning against Nur or giving up all hope on pursuing projects related to the Urdu language, the existentialism of In Custody leads Deven to come to terms with the less-than-heroic characteristics of Nur and eventually to successfully convince him to record some of his poetry.
The book suggests that this project can be meaningful even if Nur does not reveal a grand hope for Urdu literature in the way that Deven initially hopes he will. The project is meaningful on its own terms, and Deven reconciles with this truth.