1.Why?

Pius and Catra are now married and residing in the palace until the Valor mansion is ready. Pius is still stuck with amnesia and Catra still hopes to ignite their lost love. But with some jealous exes, a newborn baby and an unknown murderer among them to take care of, will Catra succeed in reminding her new husband and long lost lover how much she meant to him?

You have to read the first and second book to understand the third.