This is an intelligent novel that successfully combines elements of literary mystery (akin to Possession rather than the Da Vinci Code) together with parallel stories of the first world war and contemporary London.
Valentine Siddons is one of the first world war poets (an imaginary figure combining elements of Wilfred Owen, Sassoon, Graves et al.) who died a hero's death in 1917 rescuing a comrade in no-man's land. Elsa Myers is researching a film of his life, and starts an affair with his grandson, an academic who is writing a biography of Siddons. She discovers what she thinks are early but unknown poems of his and seeks to fit them into what is known about his life, little knowing that they will lead her to a very different story from the one she expects.
Interspersed with Elsa's story are snippets of her lover's biography, which introduce a 3rd person narrative of various episodes from Valentine's real life: his time at Oxford, the publication of his first poetry, his introduction into London literary society and the Bloomsbury group; his love affair with Constance Emberley and his time in the trenches.
This sounds complicated but actually Thynne pulls it off confidently, and allows the layers of narrative and various versions of the `truth' to themselves become part of the story she is telling. Personally I found the 1914-7 part of the story marginally more compelling than the contemporary one which was a little too obvious in some ways, but both are important to the book. With the glut of fairly recent books set in the same period, this somehow manages to remain fresh, perhaps because it spends time in London amongst the pacifist and literary crowd; but the warfare scenes are also powerful without becoming too repetitive or derivative.
The one weakness is that Elsa, supposedly a literature graduate from Oxford, cannot see that the `early' Siddons poems she finds, and which we get to read, are actually immature and just fairly bad poetry - while the story tells us that this just wasn't the case with his war poetry (which we don't get to read). But that's a small blip, which doesn't spoil the overall feel. Dramatic, emotionally reticent rather than overblown, this is a compelling and sometimes moving novel.