The question behind the question
Almost every disagreement with a tax authority stays civil and is resolved as a dispute about numbers, records, and positions taken on a return. What separates the small remainder is not the size of the discrepancy but whether the conduct looks like an error, a position that was arguable even if optimistic, or a deliberate attempt to mislead. That is a judgment made by people reading your records, your instructions to whoever prepared the return, and what you did once questions started. Anyone who tells you what a case is worth in terms of prison time before reading the file is guessing, and we will not do that in a first call either.
The moments that change direction
Certain things tend to mark a shift: investigators arriving unannounced rather than a scheduled audit appointment, a summons for bank records, your accountant being contacted separately, or a question about what you knew rather than what you reported. Two mistakes are common at exactly this point. One is explaining the situation on the spot, because those conversations are written up and become the backbone of the case. The other is assuming the accountant is a confidential channel; the protection people expect there is narrower than they think, and it often does not hold at all once a matter turns criminal.
What to bring and what we sort out first
Bring the returns as filed, whatever workpapers or spreadsheets they were built from, bank and account statements, every notice and letter you have received, and your correspondence with whoever prepared the filings. Note anything you have already told an agent. In the first conversation we work out which stage this is at, whether it is still a civil matter and how to keep it there if so, whether a corrected filing helps or hurts in your circumstances, and who else in your business or family may be drawn in. What you will leave with is a picture of the process ahead, not a number.