Single & Single by John le Carré

A lawyer from the London finance house of Single & Single is shot dead on a Turkish hillside by people with whom he thought he was in business. A children's magician in the English countryside is asked by his bank to explain the unsolicited arrival of more than five million pounds sterling in his young daughter's modest trust. A freighter bound for Liverpool is boarded by Russian coast guards in the Black Sea. The celebrated London merchant venturer "Tiger" Single disappears into thin air. - Goodreads