Dr. Jack Griffin works as an assistant for Dr. Cranley, and is engaged to his employer's daughter, Flora.
Griffin is a brilliant research scientist who discovers a formula for making a human being invisible. He feels that his poverty leaves him with nothing to offer Flora, and hopes the formula will bring him fame and fortune.
The formula entails taking opium and another drug called monocane, which was once attempted to be used for bleaching cloth but was given up as it destroyed the material.
However, Griffin is unaware that monocane has another dangerous side effect. According to Dr. Cranley, he read by chance in a German book about an experiment where a dog was injected with monocane and not only turned "dead white--like a marble statue" but also went raving mad; the English books--presumably read by Griffin-- were printed before that experiment and as a result only mentioned the bleaching power.
Griffin worked in secret trying to perfect the formula (something Kemp noted, having once walked in on him and Griffin slamming and locking a cupboard filled with instruments). When at last he perfected it and injected himself, he abruptly left so as not to be seen fading away, saying only he might not be heard of for sometime.
He went to the village in Iping, renting a room and asking for the utmost privacy, in the hope of finishing the experiment. Unfortunately he becomes extremely frustrated at not being able to find an antidote, and the drugs begin to affect his mental state. He becomes increasingly aggresive and violet, before at last revealing his invisibility and terrorizing the villagers.
Griffin makes his way to Kemp's house, explaining his experiment and his new plans to instigate a reign of terror. But first, he has Kemp drive him back to the village to retrieve his notebooks. In the process, he terrorizes the villagers again and kills a police inspector. Kemp alerts Cranley and Flora to Griffin's return before alerting the police. Griffin becomes a fugitive, who begins causing accidents and several people's deaths. He also kills Kemp in retaliation for his betrayal.
During a snowstorm, he seeks shelter in a barn and falls asleep. The farmer alerts the police and the corner him, setting the barn on fire and forcing him outside. He is shot and taken into custody. On his deathbed, he apologizes to Flora and admits he "meddled in things that Man must leave alone" before dying. The effect of the drugs dies with him, and he regains his visiblity.
- In H. G. Wells's original novel, Griffin--whose first name is not revealed--is implied to be mad from the start and not as a result of the formula. He is a gifted medical student with albinism who has no fiance, and pursues his experiments solely for his own wealth and ego. He goes after Kemp (his old schoolmate rather than his coworker), but is killed by a mob rather than the police, and Kemp lives.