1A conjunction used to introduce a result or fact that runs counter to what was just said — similar to 'however' or 'but', with a stronger nuance of 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 showed up 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'd asked for was supposed to be finished. But it hadn't even been started.