Jonah Carstairs was a Shadowhunter born into the Carstairs family. At some point in his adult life, he married Ke Wen Yu, a Chinese Shadowhunter, and together they had a son, Jem Carstairs. Not long after, Jonah was given the job of running the Shanghai Institute.
When his wife destroyed a demon nest, she inadvertantly put the Carstairs family in danger. The demon who spawned the nest, Yanluo, took revenge on them by taking the three of them captive and torturing them to death. Jonah was the first to die, and his wife followed within a day.
During their time in captivity, Jonah and his wife were forced to watch as their son was repeatedly injected with the demon drug yin fen, which gave him hallucinations. His son survived, but his body became addicted to the demon drug, which he was forced to take for the rest of his life until he became a Silent Brother.