She was trying to check up the people around her, trying to determine whether she was being followed or not. But here, in the busy part of town, that gave me no cause for worry. On a less crowded street it might have been different, though not necessarily so.
There are four rules for shadowing: Keep behind your subject as much as possible; never try to hide from him; act in a natural manner no matter what happens; and never meet his eye. Obey them, and, except in unusual circumstances, shadowing is the easiest thing that a sleuth has to do.
Assured, after awhile, that no one was following her, Mrs. Estep turned back toward Powell Street, and got into a taxicab at the St. Francis stand. I picked out a modest touring car from the rank of hire-cars along the Geary Street side of Union Square, and set out after her.
Our route was out Post Street to Laguna, where the taxi presently swung into the curb and stopped. The woman got out, paid the driver, and went up the steps of an apartment building. With idling engine my own car had come to rest against the opposite curb in the block above.
As the taxicab disappeared around a corner, Mrs. Estep came out of the apartment building doorway, went back to the sidewalk, and started down Laguna Street.
“Pass her,” I told my chauffeur, and we drew down upon her.
As we came abreast, she went up the front steps of another building, and this time she rang a bell. These steps belonged to a building apparently occupied by four flats, each with its separate door, and the button she had pressed belonged to the right-hand second-story flat.
Under cover of my car’s rear curtains, I kept my eye on the doorway while my driver found a convenient place to park in the next block.