"Solitarium" follows Arthur Morhan (Eddy Frogeais), a psychoanalyst struggling to cope with his own demons, as he intersects with various lonely individuals who are also searching for connection and meaning in their lives. Liam (Mael Nouvel) and Fiona (Cécile Dubois), among others, become entangled in Morhan's journey, leading to a complex exploration of human relationships and the blurred lines between therapist and patient.