In summer 1944, Rezso Kasztner, a Hungarian lawyer and journalist, met with Adolf Eichmann, architect of the Holocaust, in Budapest.

With the Final Solution at its terrible apex and tens of thousands of Hungarian Jews being sent to Auschwitz every month, the two men agreed to allow 1,684 Jews to leave for Switzerland by train.

It was agreed that the wealthy Jews of Budapest would pay an average of $1,500 for each family member to be included; the poor would pay nothing.

In addition to those on the train, Kasztner negotiated with Eichmann to keep 20,000 Hungarian Jews alive - Eichmann called them 'Kasztner's Jews' or the 'Jews on ice' - for a deposit of approximately $100 per head.

In other dealings, it is now estimated that Kasztner may have saved another 40,000 Jews already in camps. Bu these deals would haunt Kasztner to the end of his life.

Kasztner was later vilified in an infamous Israeli libel trial for having 'sold his soul to the devil.' While he awaited the Supreme Court verdict that eventually vindicated him, he was murdered in Israel in 1957.

Part political thriller, part love story and part legal drama, Porter's account explores questions about moral choices and the nature of Kasztner - the hero, the cool politician, the proud Zionist, the romantic lover and the man who believed that promises, even to die-hard Nazis, had to be kept.

A magnificently researched book, it is hard work in places but, like Schindler's List, it is a story that should be read - if only to understand more clearly what was going on during this painful period in history.

(Constable, paperback, £9.99)