Bitter Bloodline by Jackson Marsh

Following an accident, a schoolboy and a tattooed Romanian find themselves unexpected guests at Clearwater’s country house, Larkspur Hall.
But what if their presence is no accident? What if Mr Smith is Protectori, a member of an ancient order of assassins bent on destroying anyone who sullies the name of the Szekely people of Transylvania? And what do a runaway boy and an assassin have to do with Clearwater’s famed Easter dinner party and its guest of honour, the actor, Henry Irving?
Ancestral feuds, a pocket watch and a rare Romanian wine are seemingly random connections until Silas breaks into a London theatre, and James rescues a boy from drowning. Then, it’s a race against time to prevent a hideous murder and Archer’s ruin.