Inspector Steine had never been to the hippodrome before, so he had no idea altogethert all on what to expect.

Only when he had taken his seat next to Mrs Groynes, did it dawn on him that this was the place Seargeant Brunswick was always banging on about.

Steine was appalled, yet intrigued by the surroundings.

He started to wonder why they had chosen such a location to hold some kind ofthis surprise event for him.

He wanted to ask Mrs Groynes, but then, he wasn’t supposed to know ofabout the surprise—he had overheard Mrs Groynes talking about it.

By the time the main play was halfway through, hSteine had grown restless, finding the waiting barely impossible.

At one point, he thought he had caught a glimpse of a policeman’s uniform in one of the front rows.

However, what struck him most was that the man seemed to be surrounded by four big men, one of whom was holding an umbrella; Steine found ithat outrageous indoor.

Inspector Steine had never been to the hippodrome before,; so, he had no idea altogether what to expect.

Only when he ha'd taken his seat next to Mrs. Groynes, did it dawn on him that this was the place Sergeant Brunswick was always bangoing on about.

Steine was appalled, yet also intrigued, by the surroundings.

He wanted to ask Mrs. Groynes, but then, he wasn’t supposed to know of the surprise—he had overheard Mrs. Groynes talking about it.

By the time the main play was halfway through, he had grown restless, finding the waiting barely impossiblehis patience waning.

I think this fits better and sums up what you were trying to say.

At one point, he thought he had caught a glimpse of a policeman uniform in one of the front rows.

Inspector Steine had never been to the hHippodrome before, so he had no idea altogether what to expect.

Only when he had taken his seat next to Mrs. Groynes, did it dawn on him that this was the place Sergeant Brunswick was always banging on about.

He wanted to ask Mrs. Groynes, but then, he wasn’t supposed to know of the surprise—he had overheard Mrs. Groynes talking about it.

By the time the main play was halfway through, he had grown restless, finding the waiting bnearely impossible.

At one point, he thought he had caught a glimpse of a policeman's uniform in one of the front rows.

However, what struck him most was that the man seemed to be surrounded by four big men, one of whom was holding an umbrella; Steine found it outrageous indoors.