Clever. Angela Meerson is a scientist/mathematician from the future who has developed a portal that allows her to transport people to an alternate universe. In an effort to prevent her employer from using her device for purposes she disagrees with - AND - to prove that it works - she transports herself back to 20th century Europe. She becomes friends with Henry Lytten, a member of British intelligence during WWII who later becomes an aspiring author who develops Anterworld - a fantasy world that is perfect for Angela to test out her portal.
She builds the portal, and Rosalind, teenage neighbor and friend of Heny Lytten - accidentally goes through to Anterworld.
The story moves between Anterworld, 1960's Britain and the future where Angela originally built her portal. Characters are inter-twined.