Slow Horses kills off David Cartwright

River's grandfather David Cartwright dies peacefully in his bed at age 83 before Season 6 begins. The death happens off-screen, following the plot of Mick Herron's book Joe Country.

River learns of his loss

Diana tells River about his grandfather's upcoming funeral. River refuses bereavement leave and shows up at Slough House visibly grieving, with even Ho noticing his emotional state.

David was River's only family

The cost of David's care home depleted his savings. River's mother is absent, leaving David as his only true family besides his Slough House colleagues, deepening his isolation.

Lamb recognizes River's pain

Lamb immediately notices River's emotional state and warns him he's wound up like a spring. He tells River he needs to either let his grief out or keep it in, but can't do both at once.

“The state you're in, wound up like a spring, you're liable to go off half-cocked and get yourself in trouble.”

River's final memory of David

In a flashback, River visits David in bed as his dementia worsens. David tells River he tried to make his house a home and says, "I won't miss living without her, but I shall miss you very much."

“I won't miss living without her, but I shall miss you very much.”

River grieves at his grandfather's house

The night before the funeral, River stays at David's house in the rain. He polishes his dress shoes, eats dinner alone, and buries his face in one of David's old suits.

River delivers a coded eulogy

At the funeral, River wears David's suit and gives a thoughtful speech about his grandfather's devotion to work, love of people, and integrity. He uses transportation-coded language to honor David's secret life.

Jonathan Pryce's powerful legacy

Pryce's performance as David was phenomenal, balancing charm and humor with weighty emotional scenes. His chemistry with Jack Lowden felt genuine, and both actors elevated their performances as David's dementia worsened.

“Jonathan doesn't need to hear from me or anyone, he's an absolute titan.”

River's grief will fuel Season 6

David's death marks the end of Pryce's run on the show. River's grief will continue to follow and fuel him throughout Season 6 and beyond, shaping his character's journey.