Cable Diamond Square in rounds

[ukcrocheter]

I am super stuck on how to crochet this pattern and I really want to do it right! 
If anyone can help, I’d be so grateful. 
So the pattern begins with forming a ring and crocheting inside it to make 12 treble crochets (US double) with 2 chains in the corners (square).

However, later, the pattern reads:

Ss in first 2ch sp, 5ch, 2tr in same 2ch sp as ss, 1tr in each of next 3 sts, 1fpdtr2tog working 1 leg of st around corner 2ch from rnd below to the left, miss 1 st from previous rnd (stitch behind fpdtr2tog just made), 1tr in each of the next 3 sts, * (2tr, 2ch, 2tr) all in next 2ch sp, 1tr in each of next 3 sts 1fpdtr2tog working 1 leg of st around corner 2ch from rnd below to the right and second leg around corner 2ch from round below the left, miss 1 st from previous round (st behind fpdtr2tog just made), 1tr in each of next 3 sts, rep from * twice more, 1tr in the same sp as beg 5ch, ss in 3rd of beg 5ch.

 

I have tried so many times but I can’t get it right. Any advice would be amazing! I think if I got this round right, I would understand how to do the rest. Thanks all.

[Granny Square]

Welcome to the 'ville!  First, are you familiar with post stitches?  Because aside from this being a really loooong set of instructions, that is the most exotic part, and this one is not typical, because it's 2 post stitches together with their bottoms spaced apart so it will make a raised /\ over the fabric.   Here is a video of a split front post treble that is made in a similar way to a 1fpdtr2tog (this can be done with adjacent stitches too, not just spaced apart).

And I will admit, I crochet a lot of lace doilies with lengthy instruction lines (I just finished blocking my most recent one before checking in here, actually), and this is a looong set of instructions to keep in your head ( or maybe my memory span is shorter than it used to be).  What I usually do is work from paper pprintouts from the 'net or books I own, and I usually make pencil slash marks /  between steps, along the lines of:  

Ss in first 2ch sp, 5ch, 2tr in same 2ch sp as ss, / 1tr in each of next 3 sts, / 1fpdtr2tog working 1 leg of st around corner 2ch from rnd below to the left, miss 1 st from previous rnd (stitch behind fpdtr2tog just made), 1tr in each of the next 3 sts, / * (2tr, 2ch, 2tr) all in next 2ch sp, 1tr in each of next 3 sts /1fpdtr2tog working 1 leg of st around corner 2ch from rnd below to the right and second leg around corner 2ch from round below the left,/ miss 1 st from previous round (st behind fpdtr2tog just made), 1tr in each of next 3 sts, rep from * twice more, 1tr in the same sp as beg 5ch, ss in 3rd of beg 5ch.

As I was making slash marks, I realized that there is an error in your pattern, (or maybe you 'missed a spot' (the second leg)' transcribing it) that should have come right after the bold area--it does not tell you where to put the second leg of the 1fpdtr2tog but it does tell you where to put second in the following underlined similar area.  Also, the phrase I put in italics - this is normal, if you are in row 3 for example, and make a post stitch around a stitch in row 2, you normally skip the next stitch in row 3, because it is 'used up' by the post stitch - if you do not skip it, you will have made an increase that shouldn't be there.