Scott Lang broke into the mansion in order to get revenge from its owner, Geoff Zorick, who fired him from Vistacorp for trying to expose a fraud. Just like he did at Vistacorp Headquarters, Lang entered the mansion while reciting the steps to a successful break-in: To know the location, to know the way around security, and to be awesome.
Lang avoided Zorick's dog by feeding it with a piece of meat, and began to steal some of the jewels kept in the mansion, with the intention of giving them to his own wife Maggie. When he was about to leave, Lang could not resist the opportunity of taking Zorick's car as he remembered how Zorick used to yell at him.
Lang drove Zorick's car inside the garden, leaving the tracks of the vehicle all over the estate, until he lost control of the car and fell into the swimming pool. However, the police arrived to the mansion and arrested Lang, as he forgot the most important step in a successful break-in, to not get too carried away, or somebody would put you away.
When the police attempted to hoist the car from the pool, the cable line popped, causing the car to sink further.