Book Two of the Changes trilogy. Margaret and Jonathan rescue an American spy who has been accused of being a witch. They rescue him and sail off to Ireland in the tugboat of the title name.
Nicky finds herself in Book One of the Changes trilogy on the road, alone, her parents having disappeared in a big crowd. She joins up with a group of Sikhs, then makes her way to France.
In book three of the Changes trilogy, teen weathermonger Geoffrey and his sister Sally escape to France, but are sent back to England-ish to find out the source of the Changes. Hey, it's Merlin!