Una perdida razonable / Acceptable Loss

When the body of a small-time crook named Mickey Parfitt washes up on the tide, no one grieves. William Monk, commander of the River Police, is puzzled by the expensive silk cravat used to strangle Parfitt. How did this elegant scarf, whose original owner was obviously a man of substance, end up imbedded in the neck of a rat who richly deserved his sordid end?