The End Of Us by Olivia Kiernan

Myles and Lana Butler live on a new development in Wimbledon and are leaning on a mortgage that is just within reach after one of Myles' investments goes wrong. Their new neighbors, Gabriel and Holly Wright, are apparently very wealthy, and at an after-dinner drink the couples discuss a solution: life insurance fraud, with the Wrights helping for a cut. No one thought they were serious or that it would involve murder. Then one night Lana does not come home.