When a young man is found dead and stark naked out on the Fens, Will and Geordie discover ties to a Cambridge research project experimenting with mind-altering drugs.
Its arrogant professor is a proponent of the drug LSD in his psychotherapy sessions, but Will and Geordie start wondering whether there is more going on.
As the case proceeds, Will’s feelings of guilt about his father’s death and his conflicted feelings about Ellie start to take their toll.
Elsewhere, the Keatings suffer an awkward dinner party and the Chapman feud shows no sign of relenting.
- Geordie Keating is played by Robson Green
- Will Davenport is played by Tom Brittney
- Leonard Finch is played by Al Weaver
- Mrs Chapman is played by Tessa Peake-jones
- Cathy Keating is played by Kacey Ainsworth
- Ellie Harding is played by Lauren Carse
- Diana is played by Paula Wilcox
- Esme Keating is played by Skye Lucia Degruttola
- Larry Peters is played by Bradley Hall
- Vic Morgan is played by Ross Boatman
- Remi Adeyemi is played by Jyuddah Jaymes
- Peter Soosai is played by Akshay Sharan
- Judy Munroe is played by Stella Gonet
- Martin Adler is played by Simon Kunz
- Helen Feldman is played by Sophie Walter
- Chris Hartley is played by Jack Barton
- Professor Evans is played by Theo Fraser Steele
- Mr Hartley is played by Russell Wilcox
- Douglas Munroe is played by Andrew Bridgmont
The Keating Children are played by:
- Rose Allen
- Mason Chalke
- Harley Chalke
- Rubie-Rose Fearfield
Grantchester continues on ITV at 9pm