I have no intention of hiding a single thing.

Literal

What-one-thing hide-stand-do [intention-つもり] [topic-は] not-exist.

何一つ (なにひとつ, 'not a single thing') is an emphatic version of 何も. 隠し立てする ('to keep secrets, conceal') is a set expression. つもりはない ('have no intention of') negates the intention directly. Subject entirely omitted.