The duo, who are expecting a baby together, find themselves entangled in a web of lies shortly after Vanessa's mother Francesca arrives in Ramsay Street for a visit.
Fearing Francesca (Carmelina di Guglielmo) won't approve of her complicated personal life, Vanessa lets her mum believe that she and Lucas (Scott Major) are a proper couple.
However, events take an unexpected turn when Francesca insists that they should make their 'union' official by getting married - threatening to cut Vanessa off from the family if she doesn't agree.
Vanessa is shocked by her mother's demands, but Lucas agrees to go ahead with the idea, secretly hoping that Vanessa - newly-single after splitting from Rhys - will fall for him for real if they do become husband and wife.
Alin Sumarwata, who plays Vanessa, told TV Week: "More lies have to be made to accommodate previous lies. Inevitably, a boiling point is reached where it gets heartbreakingly messy for everyone involved."
Neighbours airs these scenes next week on Eleven in Australia, and in November on Channel 5 in the UK.