I have made it longer than ever, adding verses to show what happened when they reached their destinations. Also, a verse seemed to be missing, so I made one up - the kisses/garden verse. At the moment, I don't see why one seemed to be missing, but it's time to make my morning toast.

I didn't care for the tune, so I made up two tunes, one for Margaret and one for William. The type-face indicates when to change. Sorry about the lines breaking in the wrong place.
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1.Lady Mar'gret lay 'neath a fine feather bed, as the midnight hour drew near,
When a ghostly form in her room did tread, And to her it did appear, appear,
And to her it did appear.
"Are you my father, the king?" said she. "Are you my dear brother John?
"It's I'm your sweetheart, William, said he. Coming home from Scotland anon, anon
Coming home from Scotland anon."

2. "Oh Marg'ret, oh Lady Marg'ret," said he, "For love or charity,
Will you give me back the plighted troth that once, love, I gave thee, gave thee,
that once, love, I gave thee?"
"I'll not give you back your plighted troth nor give you any such thing,
until we go to my father's hall where ofttimes we have been, have been,
where ofttimes we have been."
And so went they to her father's hall, And as they entered in
the gates drew back of their own free will for to let Lady Margaret in, o, in,
for to let Lady Marg'ret in.
"Oh Marg'ret, oh Lady Marg'ret," said he,
"A castle ruin I see. The pennant's gone and the towers fall,
withdraw, my love, come away with me, withdraw, my love come with me."

3."Oh Marg'ret, oh Lady Marg'ret," said he, "For love or charity,
Will you give me back the kisses kind that once, love, I gave thee, gave thee,
that once, love, I gave thee?"
"I'll not give you back your kisses kind nor give you any such thing.
Until we go to the garden fair where oft the small birds sing, do sing.
where oft the small birds sing."
And so they went to the garden fair, and as their footsteps drew nigh,
the rose pulled back its thorny boughs to let these sweethearts pass by, o by,
to let these sweethearts pass by.
"Oh Marg'ret, oh Lady Marg'ret," said he, "the mist lies low on the lea.
The moon is gray and the roses pale, thy lovely face I scarce can see,
thy face I scarce can see."

4."Oh Marg'ret, oh Lady Marg'ret," said he, "For love or charity
Will you give me back the treasure troth That once, love, I gave thee, gave thee
That once, love, I gave thee?"
"I'll not give you back your treasure troth nor give give you any such thing
until we go to yon high churchyard and married be with a ring, a ring,
and married be with a ring."
He took her then to the high churchyard, and as they entered in
the gates drew back of their own accord
for to let young William in, o, in, for to let young William in.
Then out of her pocket she drew a cross and laid it on his breast,
Saying, "Here is back your treasure troth. In Heaven may your soul find rest, find rest.
In Heaven may your soul find rest."
"Oh the cold wind blows and the moorcock crows, And it's nearly break of the day,
And it's time that the dead from the living must go .
So now, my love, I must away,So now, my love, I'm away." [2x]