After the glasshouse closed

An original fictional account set in an invented public glasshouse.

Outside, rain rattled against the roof, but beneath the glass the air was warm and smelled of damp earth. Every plant had its place: palms in square tubs, orchids fastened neatly to posts and small black labels standing beside the paths. The attendant had told me to wait by the entrance while she fetched my forgotten bag. I watched her blue coat disappear between the leaves.

A row of lamps went out above the far path. A few seconds later, the next row followed. The darkness was not sudden; it advanced through the glasshouse section by section, quietly removing the paths the attendant had taken. Soon, only the lamps above me remained, reflected in the wet panes so many times that I could no longer tell which lights were real.

Somewhere among the palms, a pipe clicked. Water hissed from the overhead sprays and leaves began to nod beneath it. I knew what had caused the sound, yet the hiss seemed to travel towards me, passing from one cluster of plants to the next. A tall leaf dragged itself across the glass with a slow, papery scrape. I stepped back until my shoulders touched the locked entrance doors.

Then the blue coat appeared again at the end of the path. At least, I thought it was the coat. The shape remained perfectly still while the leaves around it shifted and shivered. I called to the attendant, but the sprays swallowed her name. One of the remaining lamps blinked out. In the brief darkness, the blue shape seemed to move closer. When the lamp returned, I saw only a broad leaf turning on its stem.

Behind me, the handle of the entrance door moved down.

How does the writer change the atmosphere from reassuring to threatening?