Sue Decker's tenure as Yahoo president was full of corporate intrigue. But it's nothing compared to her ongoing divorce in which her husband's lawyer is brandishing accusations of illegal drug use, "extramarital affair(s)" and secretly recording him at home.

Blame this altogether more sinister portrait of Decker as narcotized, philandering spy on her increasingly messy divorce, which involves a custody battle over her children. The accusations are mentioned in a September 29 letter we've obtained, sent to Decker's legal team from the San Francisco attorneys representing her husband (Click here to read the eight-page letter) .

Notice of the breakup first surfaced nearly two years ago. There didn't seem much reason to believe the parting was especially bitter. Though Decker led a series of power grabs at Yahoo, elevating herself from CFO to president and would-be CEO, her divorce generated little such noise. Divorcing couples tend to fight over money, but in April 2008 it emerged that Decker's husband Michael Dovey was not seeking alimony; he told people he was independently wealthy.

But an increasingly contentious court battle has nevertheless erupted, judging from the September 29 letter. The attorney for Dovey references hearings and letters attempting to resolve how to handle discovery, the early legal phase in which evidence is collected.

Dovey's legal team is using discovery, in part, to collect evidence concerning Decker's purported and unspecified "accusations about" her husband — including personal emails Decker may have sent referencing his conduct, "state of mind and/or mental or physical well being," according to the letter.

Some of this material may reside on old Yahoo computers, and Decker's legal team is trying to win the ability to selectively block the disclosure to Dovey's legal team of evidence as it emerges, according to the letter. Dovey's team wants much more: all potential evidence not protected by attorney-client privilege or "attorney work product protection," with particularly sensitive material handed over and protected by a confidentiality agreement.

Near the conclusion of the letter, Dovey's attorneys hint at what else they might be looking for in discovery — and what else Decker's attorneys might be trying to keep a lid on:

These sorts of allegations are relatively common in nasty divorces and custody battles and Decker, for many years a fixture of Yahoo's quarterly conference calls with stock analysts, knows how to mount a strong defense in the bright glare of the public spotlight. Still, a woman who quit Yahoo in January and just bought a waterfront home in the San Francisco Bay Area's quiet Marin County can't be happy to be caught in such a maelstrom of mudslinging. Nor, one would venture, can her former colleagues.

We've posted the full eight-page letter here.

Update: Richard Rados, who wrote the letter, declined to comment on the divorce because of "pending litigation" and added, "I don't want to contribute to ill will between" the parties involved. We left a message for Jennifer Wald, Decker's attorney, and will include any comment when/if she gets back to us.

(Top pic: Decker at an "All Hands" company meeting last year. From Yahoo Blog's Flickr account.)