A conjunction used to introduce an unexpected result or fact that contrasts with what came before (similar to 'however' or 'but', often stressing surprise).
十分準備した。ところが試験はすごく簡単だった。
I prepared thoroughly. However, the exam turned out to be very easy.
彼は遅刻しないと思っていた。ところが、今日は一時間も遅れてきた。
I thought he wouldn't be late. Yet today he arrived an hour late.
頼んだ仕事は終わっているはずだった。ところが、まだ全然始めていなかった。
The work I asked for was supposed to be finished. But it hadn't even been started.