In book seven, Harry and Hermione Apparate to the Forest of Dean, where Snape's Patronus leads Harry to the sword in a pool of ice. But how did it get there? Did Dumbledore put it there expecting Harry to find it? If so, how did Snape know Harry was in the forest? If not, did Snape put in the pool for Harry to find? Was he trying to find out where Harry was so he could lead him to the sword?
What exactly happened?
Snape leaves it on Dumbledore's (kind of) orders. This is shown in his memories during the Chapter "The Prince's Tale".
And now Snape stood again in the headmaster’s study as Phineas Nigellus came hurrying into his portrait. “Headmaster! They are camping in the Forest of Dean! The Mudblood – ”
“Do not use that word!”
“ – the Granger girl, then, mentioned the place as she opened her bag and I heard her!”
“Good. Very good!” cried the portrait of Dumbledore behind the headmaster’s chair. “Now, Severus, the sword! Do not forget that it must be taken under conditions of need and valor – and he must not know that you give it! If Voldemort should read Harry’s mind and see you acting for him – ”
“I know,” said Snape curtly. He approached the portrait of Dumbledore and pulled at its side. It swung forward, revealing a hidden cavity behind it from which he took the sword of Gryffindor.
“And you still aren’t going to tell me why it’s so important to give Potter the sword?” said Snape as he swung a traveling cloak over his robes.
“No, I don’t think so,” said Dumbledore’s portrait. “He will know what to do with it. And Severus, be very careful, they may not take kindly to your appearance after George Weasley’s mishap – ”
Snape turned at the door. “Don’t worry, Dumbledore,” he said coolly. “I have a plan…”
