Matt turned to Ysabel. Her anger was passing as quickly as it had mounted, and she seemed anxious to meet any question Matt should ask her.
"When Fingal and Cassidy came up the river in the gasoline launch," said Matt, "did they turn into the Purgatoire branch?"
"No. Pedro said that they went on up the Izaral, and got across to the encampment by another road through the woods."
"Then, if the prisoners are brought down in the launch they'll have to pass the mouth of the Purgatoire?"
"Yes."
"Dick," said Matt, "there's a chance that we can do something to that boat load of prisoners."
"What?" queried Dick, pricking up his ears.
"We can go back to the submarine, drop down the Purgatoire and wait there, submerged, until the gasoline launch comes down."
"Then what, matey?" asked Dick.