A mighty “No!” was trembling on Issy’s tongue.  But before it was uttered Burns spoke again.

“McKay’s got the best boat in these parts,” he urged.  “She’s got a tiptop engine in her, and—­”

The word “engine” dropped into the whirlpool of Issy’s thoughts with a familiar sound.  In the chapter of “Vivian” that he had just finished, the beautiful shopgirl was imprisoned on board the yacht of the millionaire kidnaper, while the hero, in his own yacht, was miles astern.  But the hero’s faithful friend, disguised as a stoker, was tampering with the villain’s engine.  A vague idea began to form in Issy’s brain.  Once get the would-be eloper aboard the Lady May, and, even though the warning note should remain undelivered, he—­

Issy smiled, and the ghastliness of that smile was unnoticed by his companions.

“I—­I’ll do it,” he cried.  “By mighty!  I will do it.  You be at the wharf here at four o’clock.  I wouldn’t do it for everybody, Sam Bartlett, but for you I’d do consider’ble, just now.  And I don’t want your ten dollars nuther.”

Doctoring an engine may be easy enough—­in stories.  But to doctor a gasoline engine so that it will run for a certain length of time and then break down is not so easy.  Three o’clock came and the problem was still unsolved.  Issy, the perspiration running down his face, stood up in the Lady May’s cockpit and looked out across the bay, smooth and glassy in the afternoon sun.

The sky overhead was clear and blue, but along the eastern and southern horizon was a gray bank of cloud, heaped in tumbled masses.

A sunburned lobsterman in rubber boots and a sou’wester was smoking on the wharf.

“What time you goin’ to start for home, Is?” he asked.

“Oh, in an hour or so,” was the absent-minded reply.

“Humph!  You’d better cast off afore that or you’ll be fog bound.  It’ll be thicker’n dock mud toward sundown, and you’ll fetch up in Waptomac ’stead of East Harniss, ’thout you’ve got a good compass.”

“Oh, my compass is all right,” began Issy, and stopped short.  The lobsterman made other attempts at conversation, but they were unproductive.  McKay was gazing at the growing fog bank and thinking hard.  To doctor an engine may be difficult, but to get lost in a fog—­He took the compass from the glass-lidded binnacle by the wheel, and carrying it into the little cabin, placed it in the cuddy forward.

It was nearer five than four when the Lady May, her engine barking aggressively, moved out of Denboro Harbor.  Mr. Bartlett, the passenger, had been on time and had fumed and fretted at the delay.  But Issy was deliberation itself.  He had forgotten his quahaug rake, and the lapse of memory entailed a trip to the blacksmith’s.  Then the gasoline tank needed filling and the battery had to be overhauled.

“Are you sure you can make it?” queried Sam anxiously.  “It’s important, I tell you.  Mighty important.”