U3A Mystery Quilt Clue THIRTEEN

The heart of the matter
Locate the fabric 1 square you've been saving and sew a Set C unit to each side of it aligned as shown.
Note the asymmetric positions of the Fabric 1 and 3 strips.
Press toward the C sets.

Ready to sew

Done

U3A Mystery Clue TWELVE

Lobsided
Take the 2 remaining HST units from Clue 10 and add a single QST to one side of each in the same alignment in both cases, either on the right or the left so that they are identical.
Press toward the QSTs.

Two lobsided units

U3A Mystery Clue ELEVEN

Getting  in a flap
Take just two of the HST units from Clue 10 and add QST's on either side as shown. (2 QST's remain).
Take care to match the two right angles as neatly as you can.
Press towards the QST's.

U3A Mystery Quilt Clue TEN

What's the point?
Take all four ABC units you made earlier and attach all four large background HST's to the long edge with the Fabric 1 squares. 
The important thing is to match the centre of the long triangle side with the centre of the ABC units. 
The triangle corners will stick out at the sides. 
Be careful with the long edge of the HST as it is on the bias and stretchy.
Press as desired.

The label should read "X 4" !!

U3A Mystery Quilt Clue NINE

Return of Set Square
Take the two Set D's and sew to two Set C's to make 2 more squares (2 set C's left).
This time Fabric 1 forms a frame around the background squre.
Press toward the D set.
Label Z square.

Z square

U3A Mystery Quilt Clue EIGHT

Set Square
Take the two Set B's and sew to two C Sets to form two squares (4 Set C units left).
Again Fabric 3 frames the background square while the strip squares are at right angles to the Fabric 1 square.
Press towards the B set and label Y square. 

Two Y square units

U3A Mystery Quilt Clue SEVEN

As easy as ABC
Take 4 Set A's (2 left)
and   4 Set B's (2 left)
and   4 Set C's (6 left)
and sew together to form ABC oblongs as shown.
Press towards Set B.
Note the background square is outlined by Fabric 3.
Label ABC and set aside.

A, B, C sets: only 4 of each are
 needed.

Sewn units

U3A Mystery Quilt Clue SIX

Take the six remaining strip squares and sew to six Fabric 1 squares at right angles but this time with Fabric 1 at the left side as shown.
Press toward the Fabric 1 square. Label Set A

Now you have four sets of units A, B, C and D which look like this:

U3A Mystery Clues FIVE

Sew a strip square at right angles to a Fabric 1 square with the Fabric 1 strip at the right as shown. Make 10 of these units and press towards the Fabric 1 square.
Label Set C.

U3A Mystery Clues FOUR

Take the remaining two background squares (none left) and
two strip squares  (16 left) and 
sew together this time with Fabric 1 parallel to the background square.
Keep together labelled "Set D".
Press toward Fabric 1.

Set D: 2 sewn units

U3A Mystery Clues THREE

Take six strip squares (eighteen remain) and six background squares  (two remain) and
sew in pairs
with Fabric 3 parallel to the background as shown.
Press toward the background square.
Label "SET B" either pinned together or in a bag.

Keeping your aide memoire close at hand helps you select the correct alignment.

U3A Mystery Clues TWO

Now cross cut your strip sets into 6.5"  squares. Don't forget the 1/2".
You should get 6 per strip set, 24 in all.

Strip squares

U3A Mystery Clues ONE

CLUE ONE
Read the hints below 
before you sew!
(NB I have aleady made some cuts as I had to allow for a mistake about which fabric was which! Ignore as, being more intelligent,  you will have continuous strips.)

Three sets of four strips with Fabric 1 on the left

Sew the strips together so that you have four WOF strip sets with Fabric 2 in the middle.

When sewing your strip sets start at the opposite end when attaching the last one. This helps to prevent bowing.
Press after each strip. Direction not critical.
However make sure your strips line up evenly at one end. This means you get the maximum amount of sub cuts. (see the second one down)

Your strip set should be 6.5" wide. Check the first seam you sew: two strips should measure 4.5" across. Adjust your seam allowance if necessary.