iBooks Library Disappeared

My iBooks Library has disappeared. There are a couple of recent items, but most have gone. I still have the items on my iPad iBooks library but can't see a way to restore them back onto my MacBook Pro.

I am running the latest operating systems all round.

Does anyone know what to do? I wondered if there might be a way to restore the library from the iPad but can't see a way to do this.

Thanks