It's possible that they are sneaking around to protect someone. Perhaps there's a young wizard or witch who is in danger from Death Eaters. Harry, being the hero he is, and Tonks, with her skills, would be trying to get this person to a safe place without being noticed. They might have to use all kinds of spells and charms to avoid being caught, and along the way, they could encounter various challenges and unexpected allies or enemies.
Well, they could be looking for something important. For example, a powerful magical artifact that could turn the tide in the fight against Voldemort. Tonks, with her shape - shifting ability, could be disguising herself and Harry to get closer to their target while they sneak around. It would be full of suspense and adventure.
In fanfiction, it could be that they are trying to discover a hidden truth about Harry's past or some ancient magic. By sneaking around, they hope to find clues that are hidden away in places like old wizarding libraries or abandoned mansions. This would add an element of mystery to the story as they search in the shadows for answers.
It could also show how Tonks and Lupin deal with the stress of the situation. They are in the middle of a war, and having a baby is a big deal. Maybe they struggle to find a safe place for their family. Lupin, being a werewolf, might be worried about how his condition could affect their child. And Tonks, being a member of the Order, might feel torn between her duties and her pregnancy.
They might face a powerful dark wizard. In fanfiction, there are often new villains created. This new dark wizard could be after something they have, like an ancient magical artifact that Harry and Ginny are protecting.
In some fanfictions, Harry Potter might learn some hidden secrets about the wizarding world's economy from the goblins. The goblins are known for their control over Gringotts and have a deep understanding of magical treasures. Harry could discover a new plot against Hogwarts related to a valuable artifact hidden in the vaults.
In the fanfiction, Harry Potter might face some challenges when visiting the goblins. He could be trying to get some information about his family's vault or a magical artifact. The goblins, being shrewd and protective of their secrets, may not be so forthcoming. Maybe he has to prove himself worthy in some way, like solving a riddle or showing respect for their ancient customs.
In the fanfiction, Harry Potter befriending the Baskilst might lead to a whole new set of adventures. Harry could introduce the Baskilst to his world of Hogwarts, and the Baskilst could show Harry some of its own unique magical abilities or knowledge. They might even start a new club or organization within the wizarding world that combines their different skills and interests.
In some fanfictions, the doctor might discover some hidden magical ailments that were overlooked in the original series. Maybe a strange magical energy imbalance that's causing his sporadic bursts of power.
He might reunite with his old friends at Hogwarts. They could have a big celebration in the Great Hall, with all the magical creatures joining in.
He might encounter some strange magical creatures that are only found underground. For example, there could be a new type of goblin or a magical mole with special powers.
He could encounter a new magical creature. The goblins at Gringotts are known to have various magical creatures guarding different vaults. Maybe Harry comes across a rare and friendly creature that helps him on his journey. For example, a small fire - breathing dragon that he befriends and it later aids him in a battle against Voldemort's forces.