Blood & Sugar — Laura Shepherd-Robinson

Waterstones Thriller of the Month for January 2020
June, 1781. An unidentified body hangs upon a hook at Deptford Dock - horribly tortured and branded with a slaver's mark.
Some days later, Captain Harry Corsham - a war hero embarking upon a promising parliamentary career - is visited by the sister of an old friend. Her brother, passionate abolitionist Tad Archer, had been about to expose a secret that he believed could cause irreparable damage to the British slaving industry. He'd said people were trying to kill him, and now he is missing . . .
To discover what happened to Tad, Harry is forced to pick up the threads of his friend's investigation, delving into the heart of the conspiracy Tad had unearthed. His investigation will threaten his political prospects, his family's happiness, and force a reckoning with his past, risking the revelation of secrets that have the power to destroy him.
And that is only if he can survive the mortal dangers awaiting him in Deptford . . .