Linda and her grandad give some parallels to Susan and 1st, in this older and younger generation dynamic.The claustrophobia of the submarine is a very terrifying concept it makes you want to hold your breath.

1st n Susan talking bout the Great Wall of china is cute, it adds to how far they have come since the exiles.

Linda’s grandad distracting her with a story is quite wholesome as the submarine submerged

The doctor meet the Slavian he says he’s never met them, but secretly knowing they keep slaves and must save earth from becoming there next target.

The aliens calling them bipeds is funny as they are snail like aliens so they don’t have legs . 

Brandis the lieutenant of the sub pulls a gun and takes control of the sub, later contacting the slarvain ship. The slarvain plan to leave their eggs on earth with the queen putting there goo on them, to help hatch the army.

The Slavain plan to open the airlock, but before the plan of getting the Tardis to take the slarvain away works. Barndis recovers from being under the Slarvains control

The story ends with Linda reminiscing about her granddad with pictures in an album 

Nice ending to a kind of boring short story in my opinion. The slavain are a bit one note I feel compared to the other short trips it just does not compare