This gives you what's going on in the beginning.

Lara's House, February 18, 2001, day.

Lara remembers the time Natla said she'll find another remant of Atlantis. Lara does some research and finds another Atlantis, which leads to another pyramid. She goes to pack up and she finds 3 large medipacks, 5 small medipacks, 6 flares, Binoculars, and a crowbar in her cabinet. She leaves all the guns in her basement. She picked 1 large medipack, 2 small medipacks, 6 flares, Binoculars, and a crowbar. She leaves and enters her basement. She quickly gets through her timed door. She climbs up a ladder leading to her treasure room. She opens a treasure chest where she stores her guns. She doesn't have her shotgun or any other guns right now. So she just got her Pistols, pulled a switch, and left her basement leading her outside. She hopped on her motorcycle and out of her yard she went.

During the ride, February 18, 2001, night.

Luckily, no obstacles had to make her get off her motorcycle. Lara had a bad feeling about the new Atlantis she is going to visit. She arrived at a river and got off her motorcycle. Atlantis was right across the river. She swam to the new Atlantis, climbed up the pyramid, and Slid down the entrance.