International Monetary Fund (IMF) investigators are arriving in Angola on Wednesday on the trail of almost $1bn which the IMF believes vanished from state coffers in 2001 alone.
The money, an internal report alleged late last year, came from oil sales, the cornerstone of Angola's foreign trade.
But instead of going to fund the country's development, more than $900m (£565m) disappeared.
Angola has insisted accounting problems, not theft, is responsible for the mismatch.
The IMF report - leaked in October 2002 - pointed to a total of $4bn which had gone missing over five years, and was scathing about what it saw as pervasive corruption and mismanagement at the top of Angolan society.
Angola has been in the IMF's bad books for some years, but is keen to return to the fold to ease a reliance on expensive short term loans to fund a ballooning budget deficit of more than 8% of the country's gross domestic product (GDP).
President Jose Eduardo Dos Santos last week appointed several reform-minded ministers to his cabinet, including a former IMF executive director, Jose Pedro de Morais, as Finance Minister.
The IMF is ready to listen.
"We're following up on pending issues from our last report and hopefully this time we'll issue a more positive assessment of economic and social policy over the past year," IMF resident representative Carlos Leite told the Reuters news agency.
But without progress on transparency and anti-corruption measures, rapprochement seems unlikely.
Angola's 27-year civil war only ended last year with the death of Unita rebel leader Jonas Savimbi.
Throughout the war, oil revenues paid the government's bills, while smuggled diamonds did the same for Unita.
But the war economy left the door wide open for corruption.
Pressure group Transparency International ranks Angola equal 98th out of 102 countries in its index of countries perceived to be least corrupt, above only Nigeria and Bangladesh.