Plaintiff Peter J. Nowicki appeals from the trial court’s judgment in favor of defendant (CCCERA) following the denial of Nowicki’s fourth amended petition for writ of mandate (petition), filed pursuant to Code of Civil Procedure section 1085. Nowicki had alleged in his petition that CCCERA and its governing Board of Retirement (Board) improperly reduced his retirement benefits retroactively, pursuant to Government Code section 31539. On appeal, he contends the trial court (1) utilized an incorrect and overly deferential standard of review; (2) ignored significant procedural errors by the Board that violated his due process rights; and (3) ignored various problems with the Board’s decision, including permitting it to misconstrue and misuse the Brown Act (Gov. Code, § 54950 et seq.). Because we conclude the Board’s decision to reduce Nowicki’s retirement allowance was an abuse of discretion, we shall reverse the judgment.