In 1970, Ashraf Marwan—a chemistry student at a British university who happened to be Gamal Abdel Nasser’s son-in-law—telephoned the Israeli embassy in London and offered himself as an intelligence asset. Marwan, who soon became an important adviser to Nasser, continued spying for Israel until 1998. In The Angel: The Egyptian Spy Who Saved Israel, Uri Bar-Joseph, an Israeli intelligence operative turned professor, tells Marwan’s story and goes to significant lengths to show—contrary to the claims of Eli Zeira, who served as the head of Israeli military intelligence during the Yom Kippur War—that he was not a double agent. Amy Newman Smith explains:
The argument about whom Marwan was actually working for cannot be untangled from the one surrounding Israel’s unpreparedness for the Yom Kippur War and the devastating casualties that resulted. . . .
Based largely on information from Marwan, by  the Israelis had developed what they called “the concept,” an intelligence paradigm that held that Egypt would not launch a war without “weapons of deterrence,” primarily anti-aircraft batteries and missiles capable of hitting Israeli cities. But by the fall, plans were coming together to partner with Syria and engage in a limited war to take back only the eastern bank of the Suez Canal. Marwan passed along information on the developing war plans to [his handler]. The paradigm had changed, but not everyone in Israel felt the shift. . . .
Zeira and his organization continued its allegiance to “the concept” despite Marwan’s warnings as well as data from other sources. . . . When Egypt pushed back the date Marwan had initially passed on for the attack, Zeira used that to discount all the information, rather than seeing changes in plans as an inevitable feature of war planning. Fortunately for Israel, the IDF chief of staff David Elazar [took Marwan’s warnings more seriously]. The traumatic encounter between Israel and the allies Syria and Egypt that began on Yom Kippur in 1973 could have [otherwise] been much bloodier than it was.