Schuck collected medieval stories and folklore and I assume the book titled Mediæval Stories (1902) which lists him as the author is such a tome. I am quoting a passage from this book:
When the traitor heard this [Blandamer has slain his lord who was abusing a woman] be became both mad and amazed, for the black knight was his lord and master, as well as of a crowd of other scoundrels. He hid his rage, though he determined within himself to be revenged, and, without their noticing it, he took a little flask containing a sleeping potion, and poured it into their goblets. They had hardly put it to their lips before all three lost consciousness, and fell into so heavy a sleep that no one could wake them. Then the traitor got up and looked at them with an exultant countenance, and, seizing Blandarner by the waist, laid him on his own horse, and took him to the castle belonging to the black knight. When he reached it he shouted to the other traitors :—
"Here I have him who has slain our master. He had with him two women apparently of noble birth, and, when we have killed this rascal, I propose that we fetch the women here and make them our slaves."
That seemed to all to be a good idea, but before they rode to the forest, they took the sleeping Blandamer and dragged him into a prison tower and threw him in.
Queen Fila and her companion were luckier than Blandamer, for, when they had slept a while, a wild cat came and began to lick their faces with its rough tongue; but, when they woke up, the animal got frightened and fled. At the first glance they cast around them they noticed that Blandamer had disappeared, and Fila at once understood what had happened.
"Ah," said she, "the traitor who gave us the sleeping potion which sent us all into a heavy sleep has assuredly carried off the faithful Blandamer. and has already, perhaps, put him to death. And we, poor women, can do nothing to help him. Let us, therefore, haste awav to avoid his seizing us also."
If you want to know the rest of the story, it should be freely available at the Hathi Trust website.