For centuries the Kingdom of England faced northeast, across the northern seas towards Scandinavia. Indeed, under King Canute, England was part of Scandinavia. But with the Norman invasion–even though the Normans were eponymously “North-men”–that changed dramatically. Within a few decades, the French and English royal trees began to intertwine, to graft branches to one another, to make love and war, sometimes at one and the same time. 

Catherine Hanley's new book Two Houses, Two Kingdoms: A History of France and England, 1100-1300 with these words:
This is a book about people.

In the twelfth and thirteenth centuries, the personal could influence the political to a great extent, and nowhere is this better exemplified than in the relationship between the ruling houses of France and England, whose members waged war, made peace and intermarried – sometimes almost simultaneously – in a complex web of relationships. These people, these kings and queens, siblings, children and cousins, held positions determined by birth; positions that often involved playing a role on the national and international stage from a very young age. Their life stories, their formative experiences and their interpersonal relationships shaped the context of decisions and actions that had the potential to affect the lives and livelihoods of millions. 
Catherine Hanley was last on the podcast in Episode 122, discussing the Empress Matilda, the subject of her previous book Matilda: Empress, Queen, and Warrior. She was born in Australia, lives in Somerset in the west of England, and when watching cricket supports “Somerset, Australia, and Tasmania—in that order.”

For Further Investigation

Two books by Catherine who are set within the period she chronicles in Two Houses, Two Kingdoms, are the aforementioned Matilda: Empress, Queen, and Warrior and Louis: The French Prince Who Invaded England,
For just a taste of what comes after the end of Catherine's book, that whole "Hundred Years War" business, you might listen to Episode 66: A People's History of the Hundred Years War
An introduction to medieval France, from the Metropolitan Museum
Medieval English timeline at the British Library
The Magna Carta Project, which Catherines says "has some good stuff about the early thirteenth century, King John, and Louis’s invasion"
Relevant primary sources for England and for France at the invaluable Internet Sourcebook