Spy Gareth Williams was unhappy in London and complained of "friction" at MI6 before he was found dead in a sports holdall, his family have said.
Cycling enthusiast Mr Williams was due to return to the West Country a week after he was found dead because he hated the "rat race" and the "flash car competitions", sister Ceri Subbe said.
She told the inquest at Westminster Coroner's Court into his death she did not believe Mr Williams would let a potential killer in his upmarket London flat, adding: "I cannot emphasise enough his conscientiousness."
MI6 were "dragging their feet" in approving his request in April 2010 to return to GCHQ's Gloucestershire HQ, she added.
Her statement added: "He disliked office culture, post-work drinks, flash car competitions and the rat race. He even spoke of friction in the office."
Explaining her comment, Ms Subbe added: "The job was not quite what he expected. He encountered more red tape than he was comfortable with."
She added: "It's impossible to do justice to Gareth's impressive character without meeting him."
Ms Subbe told how she "had a truly magical time" during her last meeting with Mr Williams for "dainty finger sandwiches" at the Ritz hotel. As a family we were incredibly close," her statement said.
Mr Williams was supposed to be on a three-year secondment in London but "as time went by his enthusiasm began to fade", Ms Subbe said. Bosses had agreed to let him leave on September 1 2010 - just a week after his body was discovered.
The naked and decomposing body of Mr Williams, 31, was found in the bath of his home in Pimlico, west London, on August 23 2010. The discovery sparked a painstaking investigation, worldwide media frenzy and several outlandish conspiracy theories.