It was a picturesque stretch of the river that confronted the Sea Scouts when the voyage was resumed. The Seine made a huge U-shaped bend, almost encircling the Forest of Roumare on the port hand, and skirting the Forests of Mauny and du Rouvray to starboard. On either bank were numerous villages, while occasionally small islands were passed. The _Olivette_ was abreast of the Obelisk at Le Val de la Haye, when her crew noticed a weird sort of craft approaching at tremendous speed. At first the Sea Scouts could not make head or tail of it. There was hardly anything to be seen but a triangular girder appearing above the apex of a double crest of spray, but the noise the quaint craft made was terrific. "It's driven by an aerial propeller," declared Peter. "I can see the glint on the blades as they revolve." Approaching at a rate of about forty-five miles an hour, the vessel passed the _Olivette_ "like a streak of greased lightning". That was Hepburn's definition. As she passed, the Sea Scouts saw that she was a hydro-glisseur, her hull composed of three rectangular floats in line ahead and supporting an aluminium cabin. Right aft was the motor with a triple chain-driven air propeller. In the bows a tiny Tricolour stood out stiffly in the breeze. Her crew consisted of two people--one, a bareheaded mechanic, wearing a blue overall, the other, a youngish man, the outstanding features of his costume being a velour Alpine hat, with a tuft of feathers, and a pair of light-yellow kid gloves. Noticing the Red Ensign flying on board the _Olivette_, the Frenchman took off his hat and made an elaborate bow. Not to be outdone in politeness, the Scoutmaster gave the order, "Alert!" and while the crew stood to attention he saluted the owner of the glisseur in scout fashion. "We ought to have dipped our ensign, I suppose," remarked Stratton. "There wasn't time," rejoined Woodleigh. "He passed before you could count five." "He's turning!" exclaimed Alan. "I say, what a heel! Oh, look! she's over!" Hepburn's exclamation directed the attention of all hands aft. Even Flemming, who was in the wheel-house, allowed the _Olivette_ to swing a couple of points out of her course as he looked astern. The air-propelled craft, extremely sensitive to her helm, had made too sharp a turn, or perhaps the mechanic had not slowed down the motor sufficiently. In any case she capsized. For a moment, quite two-thirds of the under-surface of the floats was exposed. Then, with a rending crash, the rapidly-revolving propeller blades hit the water and were shattered into splinters. The next instant the violently racing engine dipped beneath the surface. A cloud of steam, as the water came into contact with the hot cylinders, momentarily hid the scene of the disaster.