LIFELINE, by Gerry Boyle, G.P. Putnam’s Sons, 275 pages, $22.95.

A murder in a realistic rural Maine setting is served up in this third mystery by Maine journalist Gerry Boyle.

Boyle’s character in this series is Jack McMorrow, a reporter with ideals who is somewhat disenchanted with big-city journalism. McMorrow, a “birder” and an iconoclast, goes to work covering the courts for a small paper, the Kennebec Observer, to appease his longtime girlfriend, Roxanne, and promptly stirs up a hornet’s nest when he writes about a young woman in an abusive relationship.

McMorrow plunges on, angering the district attorney and sundry others, including a weak-sister editor, and soon finds himself the target of various lowlifes. Not surprisingly, the violence escalates into murder and the local police are quick to charge the abusive boyfriend. But McMorrow isn’t certain he’s the guilty one and proceeds to alienate the police as he probes further — and brings further mayhem to himself.

Boyle has an easy, clear writing style that develops the plot carefully. The action, dialogue and setting all contribute to the readability of the novel. But there is, too, a remarkable philosophical conflict that Boyle develops — the demands of journalism against the responsibility to protect innocent people. What should the journalist do when he knows his story may cause injury to innocents?

The central characters — McMorrow and his neighbor, Clair (“a real Mainer and an ex-Marine to boot”) — are reminiscent of John D. MacDonald’s Travis McGee and his sidekick, Meyer. And Boyle’s talent in characterization also brings us two endearing ladies in Roxanne and the much-abused Donna. The novel is peopled with a batch of intriguing characters. Here is how he describes his editor, Mr. Albert:

“Albert was fifty, maybe a little older. A big, stoop-shouldered guy, he had a little bit of a paunch but not much. He was wearing a bright green tie with a pale green shirt and dark green slacks, both of which complemented his reddish face. It would have been a nice outfit for St. Patrick’s Day, which was nine months away, but Albert, moving with the unhurried languor that is a sign of long-term, unchallenged authority, didn’t seem to care.”

Then there is the district attorney, Miss Tate. “She was very big, almost masculine, but very blond and carefully groomed, like a linebacker in meticulous drag.”

There is a nice, light touch — even irreverent, at times — to Boyle’s writing. When McMorrow first goes in to the Kennebec Observer newsroom, Boyle writes:

“I opened the door and stepped out into the newsroom, startling a circle of men and women who were standing around a table, feeding on doughnuts. They looked at me as if I’d just stepped into the ladies’ restroom.”

Boyle has a vivid descriptive style, too, as he describes Maine — starting with the rural town, Prosperity, in which he places McMorrow. And he sprinkles the novel liberally with pastel protraits of the Maine scene, as McMorrow periodically takes to the woods for solace.

“I moved along the ridge for a few hundred yards, picking my way between ash and arbor vitae … After fifteen minutes or so, the hardwood thickened with spruce and pine and then the softwood took over. I slipped between the stands, crossed a small stream by walking on a fallen yellow birch. In the silt by the bank, there were raccoon tracks and the single-file tracks of a fox. I kept going, continuing to head downhill, veering only when the blackberry bramble became impassable.”

Equally descriptive are the passages, frequently irreverent, describing the court scenes. The writing rings with authenticism; it should, after all, since Boyle writes a column about the courts and people in police custody that make up his “beat.” The column appears in the Central Maine Morning Sentinel and the Kennebec Journal.

There is a neat plot twist at the end that really makes this writer stand out. Boyle certainly will delight Travis McGee fans and is a welcome addition to the select list of mystery novelists who are also fine writers.

Bill Roach is a free-lance writer with Maine roots who lives in Florida.