The Secret of Loch Ness II (2010)

Eleven year old Tim plays fate and takes a flight to Scotland with his father Eric. They were happy there two years ago, shortly before his mother Anna died in a car accident. In Scotland, Tim combs through the Hartspring Castle and whose crypt. He finds a chart with Celtic characters, that refers to the true existence of the legendary Loch Ness monster.

Unfortunately the movie The Secret of Loch Ness II is not yet available on HBO Max.