Foul Pray

A Monastery Murder of the 5th century
It's 419 A.D. The Roman legions have abandoned Britannia, leaving their former subjects to fend for themselves. A few miles south from Hadrian's Wall lie the city of Coria and the nearby, St. Antony's Monastery, home to misfits and men hiding from their dark pasts, under the supervision of Abbot Mutter and his second-in-command, Prior Tomas.
Clodius, an often naughty, superstitious, nineteen-year-old novice, nears completion of his novitiate. An orphan, Clodius was abandoned to St. Antony's care by his two crooked, unloving brothers. Clodius's best friend is Eutychus, a mischievous novice who is biding his time, living off the monastery's benevolence until something better comes his way.
When the novices sneak off to a forbidden lake, disobeying Abbot Mutter's order, Eutychus is bitten by a viper, and Clodius stumbles upon Brother Adalbert's floating corpse. There's much to explain, and no lie that Clodius can muster will satisfy the abbot's wrath. So, while his friend convalesces, Clodius is punished with long hours of penance at the church's altar. Deep in the night, as vermin scurry across the rafters, Clodius hears God's whisper, "Find the murderer."
Why God would choose him, Clodius can't imagine. More of an impenitent reprobate than any kind of holy instrument, Clodius feels unworthy, his unfitness for the divine quest made even clearer by the decidedly unholy thoughts he's been having about a young woman at Coria's market. And if God really wanted him to succeed in this mission, he could have made things a little easier. No one will admit to knowing much about Adalbert or the possible reasons for his death; and then, to make things worse, the alarming news arrives that 1,000 bloodthirsty Picts have breached Hadrian's Wall and are headed toward Coria. Whatever God is thinking, Clodius had better solve the crime quickly because there won't be anybody left alive to care about justice for poor Adalbert once the Picts arrive.