As Watergate unfolded, Nixon and his men pressured Gray to delay the investigation, destroy documents and deliver raw FBI files to the White House. It cost Gray his job.
"In the service of my country, I withstood hours and hours of depth-charging, shelling, bombing," Gray said. "But I never expected to run into a Watergate in the service of a president of the United States -- and I ran into a buzzsaw, obviously."
All the while, Felt was leaking information gathered by Gray's FBI to Woodward and Bernstein.
Gray still wonders how Felt grew to distrust him, though he suspects it stemmed from knowledge of an attempt by Nixon aides to get Gray to delay an FBI investigation.
The plot was captured on the now-infamous "smoking gun" tape, on which White House chief of staff H.R. Haldeman, with Nixon expressing agreement, planned to block Gray's FBI investigation by calling in the CIA.
"The way to handle this now," Haldeman said on the tape, "is for us to have Walters call Pat Gray and just say, 'Stay the hell out of this. This is, uh, business here, and we don't want you to go any further on it.' That's not an unusual development. … And that would take care of it."
Gray said the order came directly from White House adviser John Ehrlichman, "and it was blunt, too."
"He said, 'I want you to stop the exercise on that money trail until we can sort out the facts, and the CIA will be in touch with you,' " Gray said. "And the CIA was indeed in touch with me."
Nevertheless, with Felt's urging, "We continued on, and we penetrated it," Gray said, adding, "I didn't need Mark Felt to tell me that I had to press on. I knew what was at stake here."
Gray also was starting to get phone calls from the White House. After a call on June 28, 1972, Gray ended up meeting with Ehrlichman and White House counsel John Dean about the contents of Hunt's safe.
"I was presented an envelope; I think it was about 8½ by 11," Gray said. "Dean told me that this envelope contained papers that were removed from Howard Hunt's safe, they had nothing to do with the Watergate investigation, but they must not see the light of day."
Gray said he didn't look at the papers at the time, instead putting them in a locked, "heavily secured" FBI storage unit.
"I was not really interested in what was involved there," Gray said. "They told me it didn't involve Watergate."
Though he believed Hunt was involved in the Watergate break-in, he took Nixon's advisers at their word because, "I'm operating there on this presumption of regularity that these guys are not trying to sandbag me, and I didn't have for a moment any feeling that they were setting me up."
Several months later, Gray said he finally looked at the papers as he burned them in a Connecticut fireplace.
"The first set of papers in there were false top-secret cables indicating that the Kennedy administration had much to do with the assassination of the Vietnamese president," Gray said. "The second set of papers in there were letters purportedly written by Senator Kennedy involving some of his peccadilloes, if you will."
Gray said the stack of papers he destroyed was a thin one.
"All of the world thinks that I had buckets of files destroyed," he said. "I didn't."