Gilbert Morris 
High Calling (House of Winslow Book #37) 

Katherine Winslow feels that God has a specific plan for her life–and that it will be something very grand. She rejects the idea of marriage, believing it would only get in the way of the high calling God has in mind for her.When Kat is sent to London for missionary training, she is reunited with Derek, a former beau now in the RAF. As the Battle of Britain heats up, Derek is missing in action, leaving Kat to wonder about the certainty of her calling.The High Calling will capture readers attention with page-turning adventure and inspiring romance.