The Swiss bank account. Usually a staple of international spy thrillers, it’s now getting top billing in a venue that’s more often known for dreadfully boring motions on matters of administration: a subcommittee of the United States Senate.

Read: FATCA squeezes American clients

The Permanent Subcommittee on Investigations has released a report that shines a light on the dubious dealings of one bank in particular: Credit Suisse.

“When asked how many of the U.S.-linked accounts opened in Switzerland were hidden from the United States, Credit Suisse told the Subcommittee that it has been unable to determine or estimate that number. When asked how much money was involved in the undisclosed Swiss accounts, Credit Suisse was again unwilling to answer.

“But any one of three methods for estimating the extent of the tax compliance problem at Credit Suisse shows that the vast majority of the 22,000 Swiss accounts opened for U.S. customers — between 85 and 95 percent – may have been hidden from U.S. authorities.”

The undeclared accounts could hold between five and 12 billion CHF (approximately US$5.5 and 13.5 billion).

Read: T1135 gets another facelift

Credit Suisse, says the report, has turned a blind eye to evidence of U.S. clients dodging the taxman. And the bank “continues to resist calculating the extent to which its Swiss accounts were used to facilitate U.S. tax evasion.”

But it gets better. Here’s the report’s description of how a certain “Client 1” took care of business at Credit Suisse:

“In order to tend to the Credit Suisse account, Client 1 usually travelled to meet [Credit Suisse banker] Mr. Bergantino in Switzerland on an annual basis. Typically, Client 1 informed Mr. Bergantino, in advance of the trip, of plans to visit Switzerland. At each visit, upon arriving at the bank, Client 1 met a Credit Suisse employee in the lobby. When they took an elevator to another floor, Client 1 observed that the elevator had no buttons and was controlled remotely.

“A bank representative then escorted Client 1 to a nondescript meeting room, painted white, to meet with Mr. Bergantino, instead of meeting in Mr. Bergantino’s office. As was the usual practice, Client 1 viewed the account statements, and then discussed their contents with Mr. Bergantino.

“Mr. Bergantino then offered Client 1 additional financial products. At the close of each visit, Client 1 signed an order to destroy the account statements that had been reviewed. Whenever Client 1 was visiting the bank, Credit Suisse offered an opportunity to withdraw funds in cash, though Client 1 did not recall ever doing so.”

Read: Hidden camera reveals offshore tax scams