Siren's song (5th/ final book)

Last time we saw Syreana she was going on her very own quest. What that quest was for we do not know.
But now we will find out,
Why she left?
And why couldn't she take Jack?
Although when Syreana and Jack meet again, Syreana will have a few questions herself.
The biggest one being...
"Who exactly is Angelica?"