BOOK REVIEW / Prisoners who dreamt of love and flowers: Love letters from cell 92 - Dietrich Bonhoeffer and Maria von Wedemeyer: HarperCollins, pounds 19.99

'WE HAVE been mute witnesses of evil deeds,' wrote Pastor Dietrich Bonhoeffer at the end of 1942. 'Are we still of any use? Will our spiritual resistance to what is enforced on us still prove strong enough, and will we still be honest enough with ourselves to rediscover the road to simplicity and integrity?' He was given no chance to find out. Three months later, Bonhoeffer was arrested by the Gestapo and sent to the military prison of Berlin-Tegel. Fifteen months later he was dead, hanged together with others who had plotted with Admiral Cabaris against Hitler.

The story of Bonhoeffer's last year is now told, in greater detail than has been possible before, through the letters he exchanged with Maria von Wedemeyer, to whom he had become engaged shortly before his arrest. In keeping with social proprieties, and in any case separated by the war, they had never seen each other alone; nor were they ever to do so, as the few prison visits allowed them were watched over by guards. Both were extremely conscious that they barely knew each other. Yet these letters, edited by Maria's sister, Ruth-Alice von Bismarck, testify to a growing closeness and happiness, what Eberhart Bethge, Bonhoeffer's close friend, has called a 'love story rich in denial'.

Always loving, both emerge as strong characters and committed Christians, with clear ideas about morality and behaviour. Neither wasted time on regrets or complaints. Bonhoeffer, writing not just what were to be his last theological thoughts, but also fragments of a play and some fiction, reverted 'outwardly and inwardly . . . to the simplest aspects of existence'. Maria, whose early letters are almost childlike in their excitement, became increasingly reflective. As a portrait of a relationship evolving despite almost unimaginably tough circumstances, Letters from Cell 92 is a remarkable book.

At the time of his arrest, Bonhoeffer had been banned from his ministry because of his outspokenness. He was already involved with the resistance. Maria, who had just left school, was 18, Bonhoeffer 37. Because their letters had to pass before a censor, they contain little about the war. Against a background of personal losses - Maria's father and brother were both killed, while the Bonhoeffer parents were to see two sons and two sons-in-law executed - they talked of everyday thoughts and events and asked questions they had had no time to put before. Did Bonhoeffer like dogs? What did Maria feel about skiing? Their letters tell of the struggle of many ordinary Germans to hold on to a way of life that they desperately wanted to believe was not about to disappear.

Ruth-Alice von Bismarck's footnotes are informative, but she has chosen to reserve the background story for a separate 80-page section at the end. It might have made for easier reading had these fascinating notes been interspersed among the letters, even at the cost of disturbing the thread of increasing intimacy between Bonhoeffer and Maria.

Of all the themes touched on during their year-long correspondence, the most poignant concerns their plans for the future. In the absence of shared memories, and with the impossibility of discussing their immediate fears, both Bonhoeffer and Maria turned to questions of what sort of wedding they would have and which flowers both preferred, dreaming of what Bonheoffer called a union of two people who would stand 'shoulder to shoulder like an impregnable bulwark'. It was as if at times only fantasy made the horror of their present lives tolerable.