Death and the Assassin's Blade

The man was not meant to die; the daggers were only theatrical props, plastic and harmless.
A summer's night, a production of Julius Caesar among the ruins of an Anglo-Saxon fort. Detective Inspector Tremayne is there with his sergeant, Clare Yarwood.
The assassination scene, the man collapses to the ground, Brutus defending his actions; Mark Antony's rebuke.
It was meant to be high drama, not murder, but someone's switched the daggers.
The man's death, in plain view of two serving police officers.
They're a disparate group, the amateur actors. One's an estate agent, another, an accountant. And then there is the teenage man, the gay, the funeral director. And what about the women? They could be involved.
They've all got a secret, but which of those on the stage wanted Gordon Mason, the actor who had portrayed Caesar, dead?