What thoughts keep Peter going during the swim?

From the text:

I mustn't give up. I mustn't give up. I think I panted the words aloud, above the roaring in my ears. Everything depended on my reaching that thin line of gray shingle, that fringe of oaks and pines. If I gave up now, and let myself slip down into the sweet peace of green water, the Queen would be murdered and the kingdom thrown into anarchy. Thousands of Enghshmen would die in the quarrel. English homes would flare skyward, English women and children would run shrieking to the safety of forest and fell, and the horror our people had not known for years would come again.

That was what kept me swimming.