In The Shadow Lines, darkness could symbolize adventure. At the big house, Ila grabs hold of the narrator. She wants to hide from all of the people. Their quest is infused with darkness. The stairs disappear into the darkness, the narrator spots shapes rising from the darkness, and the two have to stumble through the darkness to play Ila’s game, Houses. As the narrator is drawn to Ila, the chance to be with her in the darkness is thrilling. He describes his stomach as “churning with a breathless hide-and-seek excitement.”
The possibility that darkness symbolizes adventure is reinforced later on with Tridib. In London, Tridib remembers darting across the road and almost causing a car accident. He runs into a bombed-out cinema. A crucial part of the cinema’s intrigue is its darkness. The darkness of the movie theater leads to further adventure and sensation as it's tied to Tridib seeing two people have sex.
Alternately, darkness might symbolize pain and trauma. The narrator doesn’t understand why Ila’s game, Houses, has to be played in the dark. He wonders why they can’t play it outside or in the drawing room. Ila insists that it has to unfold “somewhere dark and secret.” Here, darkness links to the abuse that Ila experienced in London. Her mistreatment is central to the game and the story that she imposes on her doll Magda. Ila grapples with the bullying she had to deal with by placing her doll in a similar situation. After Ila finishes the story, she cries, which lends credence to the claim that the game has to be played in darkness, corresponding to deep, personal suffering.