Opening-night jitters changed to opening-night horrors five minutes before actor Ted Cancila collapsed in the first act of “Angel Street” Tuesday at Acadia Repertory Theatre. The actors had started to go up on their lines, and the delivery got bumpy. Back in the office, director Ken Stack winced as he listened to the progress of the show over the monitors.

Then Cancila uttered the fateful line, which turned out to be eerily ironic. “Do you know, Mrs. Manningham, it has occurred to me that you’d be all the better for a little medicine?” his character said to another, who was in a fit of distress. At that moment, Cancila faltered, the lines got muddy, he was caught by a quick-moving stagehand who appeared from behind a door, and the house lights came up.

“We’re having technical difficulties,” the stage manager called out, and everyone took an impromptu intermission. During that time, a doctor in the house tended to Cancila, who had succumbed to exhaustion after closing one very demanding show over the weekend and heavily rehearsing another in the meantime. Within minutes, the audience was comforted with news of Cancila’s speedy recovery and was promised the rest of the show shortly.

When the lights came up on the actual event 15 minutes later, Cancila won a heroic round of applause for triumphantly proving that the show must go on.

“These things happen sometimes,” Stack said during a second intermission.

Behind Stack’s back, a man from the audience whispered, “The intermission was more exciting than the show.”

It’s an unfortunate truth, and one that is admittable only because Cancila’s misfortune was temporary. The plot of Patrick Hamilton’s 1939 melodrama “Angel Street,” which was adapted for screen as the film “Gaslight,” is dreadfully predictable. There are lots of genuinely funny lines, most of which are delivered by Cancila, who plays a flamboyantly nutty detective. And these lines give sustenance. But as a Victorian thriller, the emphasis is less on the thrill these days.

An early entry in the thriller genre, “Angel Street” is about the vulnerable and haggard Mrs. Manningham, who doesn’t suspect that her husband is a murderer obsessed with locating some rubies hidden in their London home. When a mysterious detective arrives seeking her help to pursue an unsolved crime, she is so close to the brink of insanity that she can’t figure out whom to trust. In fact, you’ll get the picture long before she has a clue.

With a set awash in ruby red, Stack emphasizes the psychological aspects of the show, and costumer Jodie Osgood laces it up in Victorian garb. A menacing mood is set by gaslights and intermittent sentimental music — not to mention the old sideways glance by various characters.

Given the events on opening night, it’s hard to say what the overall dramatic effect of the show might be when the cast is cooking. Leslie Smith, as Mrs. Manningham, was often painfully pathetic, and that wore thin quickly. The role is a real monster because the character is rather pitiful, and Smith doesn’t get much beyond dowdiness to offer a sympathetic person. Alan Gallant, as Mr. Manningham, was thankfully understated and solid in presenting an unaffected and devious villain. Supporting performances by Kathleen Lake as a perceptive and discreet maid, and by Eliza Jacobsen as a kittenish house girl, stayed in the background (except when Jacobsen brought a tad too much contemporary brattiness to her flirtations).

Still, it appears as if Cancila is a major force behind the success of this show. Gallant does his straight part and does it well, but Cancila adds the humor and eccentricity that are the hallmark of plays in this tradition.

Halfway through the show, the cast was one-upped when a bug the size of a hummingbird took flight among the stage lights. It had been let in when all the doors and windows were opened in an effort to cool down the theater after a hot day. It was a slightly pesky inconvenience and aroused nowhere near as much concern as the earlier misfortune. The bug merely got a few programs waving through the air, but it didn’t stop the show.

Opening night was filled with surprises. Too bad they didn’t come from the script. Probably the performances — without the dramatic interruptions — will carry this show to success, but otherwise the plot leaves you thinking that the term “Victorian thriller” might, indeed, be an oxymoron.

“Angel Street” will be performed 8:15 p.m. Tuesday-Sunday through July 27, 2 p.m. July 28, and will be reprised Sept. 10-15 at Acadia Repertory Theatre in Somesville. For tickets, call 244-7260.