A departure on the haunted house motif, and infinitely less viscera splattered than their franchise startup Saw, James Wan and Leigh Whannell’s Insidious is worthy enough to be a good date movie. The latter’s script for director Wan reflects the Aussie friends’ shared enthusiasm for the popular “possession” genre while “proving that I can do more than just blood and guts horror.”

With a final frames kicker that screams Sequel, the film divides into  halves held together less through mood, continuity and character than by dark palette and jarring piano and screeching violins.

More traditional and more effective, the first part in fact depends on character, or rather on the acting of Patrick Wilson and also-Australian Rose Byrne as Josh and Renai Lambert, he a schoolteacher, she a composer. Comfortable with one another if slightly harried about settling in, the couple is still unpacking in the three-storey house to which they have moved with young sons Dalton and Foster (Ty Simpkins, Andrew Astor) and a baby daughter.

Creaking doors and floors are natural in the wooden house, along with a misplaced shipping box, and unintelligible whispers and intercom rants may be drafts in the old structure, while hurrying figures glimpsed in hallways or windows lead to expectations of yet another tale of an unhinging female. An exploring Dalton’s fall from a broken attic rung also seems explicable, and so at first is his lapsing into unconsciousness by the following morning.

Hospital doctors, however, cannot pinpoint this older son’s condition, not a coma or alteration in measurable vital indicators but rather some sort of absence of the inner person. Three months later he is home, unresponsive as ever and hooked up to monitors. Home alone with the boy and baby, with Josh working late to avoid the issue, Renai hears and glimpses presences, which inclination attributes to a guilt-ridden psyche. Additional oddities fail to convince Josh, but bloody clawlike handprints on sickroom bedsheets drive her outside and to demand another move.

SPOILER ALERT

In the new, more modern and sunlit house, Josh’s mother Lorraine (Barbara Hershey), who helps out, believes her daughter-in-law’s story but can’t help feeling troubled. The change in venue proves no deterrent, as the inexplicable continues, so she calls in Elise Rainier (Lin Shayne), an old friend and paranormal investigator and exorcist.

Here the thrust changes and sags, not so much from budget-driven effects as from departure from the plausible opening. Nor does the film benefit from comedic Olsen-and-Johnson Ghost Catchers/Murray-Aykroyd-and-Ramis Ghostbusters technical assistants Steven “Specs” and Tucker (writer Whannell and Australia’s burly Angus Sampson) with their ectoplasm Geiger counter and ghost gizmos. Josh balks and sends the trio packing after a gas-mask séance, popping bulbs and b&w inserts but is convinced after noticing Dalton’s confirmatory crayon drawings.

Her face illuminated from below, Elise expounds on astral projection, a transference or personality traveling to “the Further,” a realm of evil inhabitants who seek return to this world through the bodies of living beings. Thus, it is the boy instead of either residence who is “haunted” and in danger of being lost for good where “there’s no way out.”

Lorraine affirms this, disclosing what has been behind her knowing looks. Soul travel is inheritable, since as a youngster Josh had gone through the same and was rescued by Elise, the experience erased from his memory but manifest in a horror of being photographed. Now, to save his son, he must again journey to a dark world peopled by giggling spooks reminiscent of the sisters in The Shining’s Overlook resort corridors and of Dickens’ mad Miss Havisham, lorded over by the demonic flame-faced figure to, of all things, Tiny Tim warbling “Tiptoe through the Tulips.”

Less hyped than studios’ The Exorcist and Poltergeist and their silly spawn, less dependent on gut-churning effects, and probably destined for less box office, Insidious benefits from being buoyed by its first hour or so. Overall a better watch than teentalk advance publicity would lead one to expect, it has already been included in Film Comments Selects at the Film Society of Lincoln Center.

(Released by Film District and rated “PG-13” for thematic material, violence, frightening images and brief strong language.)