One in Three by Tess Stimson

Both of them loved him. One of them killed him . . .

Louise has had to watch her husband, Andrew, start a new family in the four years since he left her. The ‘other woman’ is now his wife – but Louise isn’t ready to let Caz enjoy the life that was once hers, or to let go of the man she still loves.
As Louise starts to dig into Caz’s past, the two women’s pretence of civility starts to slip. But in trying to undermine each other, they discover more about the man they both married.

And when Andrew is murdered at a family party, both women are found standing over the body.
And when Andrew is murdered during the anniversary celebrations, both women are found standing over the body.
It’s always the wife. But which one?