"Letters and Papers from Prison" (Vol. 8 in the Dietrich Bonhoeffer Works). This is the volume wherein Bonhoeffer (I believe) has been most misunderstood and misrepresented (though some would certainly disagree with my conclusions). His notion of "religionless Christianity" deserves a careful consideration and not a knee-jerk reaction as is so often the case. I would encourage anyone interested in (the later...more controversial) Bonhoeffer to find a copy and read it thoroughly.
Here are the links to the pdf files of the Introduction, the Prologue, the First Chapter, and the Table of Contents. Happy reading! :-)