Loose lips aren't the only thing that can sink ships…but sending submarines into Sirena's seas can only lead to one thing: war.

William said that Singapore would fall, but Sirena didn't expect it to happen while she was there.

With a submarine on her tail as she tries to preserve her grandfather's precious treasure, Sirena finds herself on the other side of the ocean from her daughters…and with no choice but to fight to protect the human city she once called home.

With the human world at war on land, air and sea, one siren will answer the call. But it will take more than one siren to win this war…