Meanwhile, Morse's stepmother Gwen - the mother of Joyce - is being treated in a nursing home where a Dr Desmond Collier (Jason Isaacs), a pioneering chemist who has invented a new anti-ageing drug, 'seraphics', which work by expanding the blood vessels which leading to the brain, allowing blood to move more freely.
Both Marilyn and Jacko are found to have ingested the same pill before their death, although it is not immediately recognizable to the pathologist. A friend of Marilyn's, Vicky Wilson (Liza Walker), goes missing, which adds a degree of urgency to the investigation. Morse and Lewis learn more about rave culture from a younger drugs squad officer and they manage to discover a periodical unofficial 'rave' event called CHERUB which Marilyn, Vicky and Jacko have been attending.
Morse and D.S. Lewis (Kevin Whately) observe, concealed, a rave at a leased stately home. Morse is somewhat disappointed to see no alcohol being drunk. They do discover, however, that a new experimental drug is being used. The drug in question is currently in testing; there is some controversy about the long-term effects on young people, and whether such considerations are relevant as the medicine is intended for the elderly. As the medicine increases blood flow, and therefore the supply of oxygen to the brain, it helps relieve some symptoms of ageing in the elderly but leaves young people, whose blood vessels do not need widening, with a feeling described by the pathologist as 'a feeling of extreme clear-headedness.' Vicky, when discovered, describes the effects of seraphics as being a feeling of 'seeing the whole world and loving everybody in the world', the comedown of which can cause such terrible depression it is believed to have led to the two suicides.
The drug dealer is observed by Morse and Lewis - it is Dr Collier, but he is killed in a car crash as he attempts to escape. Morse subsequently declares he hopes the 'killer' is in Hell, to which Lewis responds, 'You don't believe in Hell, Sir.' Morse responds that he wishes he did, commenting on how awful it is to be fifteen. There is some reference to his teenage years and his uneasy relationship with his father.