On Christmas Eve, in the stifling heat of a Latin American country, a nun collapses at prayer. In agony, she feverishly cries out words no-one can understand.

At the same moment, thousands of miles away in London, a young woman wakes panic-stricken in her prison cell. Words of a strange language are screaming in her head: something dreadful is coming, and she's a child again, tense with fear.,

What links these two women in a way that is inexplicable, threatening - and, ultimately, deadly? As the nun nears death, a Jesuit priest tries to find out, uncovering the hidden past. In doing so he is forced to face his own demons, releasing emotions long repressed and denied...and learns no-one ever keeps a secret as well as a child.