abreast of
it. Although it was very dark, they now floated on their backs by
the piece of timber, so as to show as little as possible to any who
might be on the lookout, for of all objects the round outline of a
human head is one of the most easily recognized.

Presently they came, as they had expected, to a floating boom,
composed of logs of timber chained together. Here the piece of
timber came to a standstill. No talk was necessary, as the course
under these circumstances had been already agreed to. The petards
and other objects were placed on the boom, upon which Rupert, as
the lightest of the party, crept, holding in his hand a cord
fastened round the log. Hugh and Gerald Dillon now climbed upon one
end of the log, which at once sank into the water below the level
of the bottom of the boom, and the current taking it, swept it
beneath the obstacle. Rupert's rope directed its downward course,
and it was soon alongside the boom, but on the lower side.

The petards were replaced, and the party again proceeded; but now
Hugh swam on his back, holding a short rope attached to one end, so
as to keep the log straight, and prevent its getting across the
mooring chains of the boats forming the bridge; while Rupert and
Gerald, each with a rope also attached to the log, floated down
some ten or twelve yards on either side of the log, but a little
behind it. The plan answered admirably; the stream carried the log
end-foremost between two of the boats, which were moored twelve
feet apart, while Gerald and Rupert each floated on the other side
of the mooring chains of the boats; round these chains they twisted
the ropes, and by them the log lay anchored as it were under the
bridge, and between two of the boats forming it. If there were any
sentries on the bridge, these neither saw nor heard them, their
attention being absorbed by the expectation of an attack upon the
breaches of Fort Saint Michael.

The party now set to work. With the gimlet holes were made a couple
of feet above the water. In them the hooks were inserted, and from
these the petards were suspended by ropes, so as to lie against the
sides of the boats, an inch only above the water's level. The fuses
were inserted; and all being now in readiness for blowing a hole in
the side of the two boats, they regained the log, and awaited the
signal.

The time passed slowly; but as the church clocks of the town struck
eleven, a sudden outburst of musketry broke out roun