tā / běn lái / zhǐ shì / xiǎng / bāng / péng you / yí ge / máng / méi xiǎng dào / wù shàng zéi chuán

他本来只是想帮朋友一个忙，没想到误上贼船。

He only meant to help a friend, but unexpectedly got involved in a hopeless venture.