The Slowworm's Song by Andrew Miller

From Costa Award-winning and Booker Prize-shortlisted author Andrew Miller comes a tender tale of guilt, trust, and a father's yearning to atone.
A harmless-looking letter drops onto the doormat in Stephen Rose's Somerset home like an unexploded bomb. It is a summons to an inquiry in Belfast, asking him to give testimony about his participation in a disastrous event during the Troubles–one he has long worked to forget.
An ailing ex-soldier and recovering alcoholic, Stephen has just begun to build a fragile bond with Maggie, the adult daughter he barely knows. For two years, he has worked hard to earn her trust, but the tragedy of what occurred back in the summer of 1982 has the power to destroy their new relationship. To buy time, he decides to write her an account of his life. Part explanation, part confession, it is also a love letter to Maggie.
When the moment comes that he must face what happened in Belfast that...