When an Argentine math student discovers the smothered body of his landlady, conventional wisdom points to a family member with the most prosaic of motives.

But then renowned logician Arthur Seldom, author of a book on the mathematics of serial killers, tells of a strange note left in his mailbox. The note indicates that the murder is the first in a series linked by a mysterious pattern. Each new death is accompanied by a different mathematical shape. It seems that the serial killer can be stopped only if someone can crack the next symbol in the sequence. The leading Oxford logician and the math graduate team up on a quest to crack the cryptic clues.